Electrosurgical apparatus having a curved distal section

ABSTRACT

Apparatus and methods for advancing and retracting a medical instrument within an introducer device, wherein the instrument includes a distal tip, a distal linear portion, a first distal curve, a substantially linear inter-curve portion, and a second proximal curve. The length of the distal linear portion and the angle of the first curve determine the position of the distal tip within a lumen of the introducer device, such that the distal tip occupies a substantially central transverse location within the lumen and the distal tip avoids contact with the introducer device. The length of the inter-curve portion and the angle of the second curve determine deflection of the distal tip from a longitudinal axis of the shaft when the second curve is extended distally beyond a distal end of the introducer device. Also, methods and apparatus for treating an intervertebral disc by ablation of disc tissue. A method of the invention includes positioning at least one active electrode within the intervertebral disc, and applying at least a first high frequency voltage between the active electrode(s) and one or more return electrode(s), wherein the volume of the nucleus pulposus is decreased, pressure exerted by the nucleus pulposus on the annulus fibrosus is reduced, and discogenic pain of a patient is alleviated. In other embodiments, a curved or steerable probe is guided to a specific target site within a disc to be treated, and the disc tissue at the target site is ablated by application of at least a first high frequency voltage between the active electrode(s) and one or more return electrode(s). A method of making an electrosurgical probe is also disclosed.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority from U.S. ProvisionalApplication No. 60/224,107, filed Aug. 9, 2000.

The present application is related to PCT Application No.PCT/US00/13706, filed May 17, 2000, now abandoned, which claims priorityfrom U.S. Pa. No. 6,264,650, issued Jul. 24, 2001, which is acontinuation-in-part of U.S. Pat. No. 6,203,542, issued Mar. 20, 2001,and U.S. Pat. Nos. 6,063,079 and 6,159,208, issued May 16, 2000 and Dec.12, 2000, respectively, each of which are continuation-in-parts of U.S.Pat. No. 6,109,268 issued Aug. 29, 2000, which is a continuation-in-partof U.S. Pat. No. 5,697,281, issued Dec. 16, 1997, the completedisclosures of which are incorporated herein by reference for allpurposes.

The present application is also related to U.S. Pat. No. 6,277,112issued Aug. 21, 2001, which is a continuation-in-part of U.S. Pat. No.5,902,272, issued May 11, 1999, the complete disclosure of which isincorporated herein by reference for all purposes.

The present application is also related to commonly assigned U.S. Pat.No. 6,179,836, issued Jan. 30, 2001; U.S. Pat. No. 6,045,532, issuedApr. 4, 2000; U.S. Pat. No. 6,142,992, issued Nov. 7, 2000; U.S. Pat.No. 6,149,620 issued Nov. 21, 2000; U.S. Pat. No. 6,620,155 issued Sep.16, 2003; U.S. Pat. No. 6,363,937 issued Apr. 2, 2002; U.S. Pat. No.6,190,381 issued Feb. 20, 2001; U.S. Pat. No. 6,355,032 issued Mar. 12,2002; U.S. Pat. No. 6,210,402 issued Apr. 3, 2001; U.S. Pat. No.6,159,194 issued Dec. 12, 2000; U.S. Pat. No. 5,873,855 issued Feb. 23,1999; U.S. Pat. No. 5,843,019 issued Dec. 1, 1998; and PCT InternationalApplication, U.S. National Phase Serial No. PCT/US94105168, filed on May10, 1994, now abandoned; now U.S. Pat. No. 5,697,909 issued Dec. 16,1997, which was a continuation-in-part of U.S. patent application Ser.No. 08/059,681, filed on May 10, 1993, which was a continuation-in-partof U.S. Pat. No. 5,366,443 issued Nov. 22, 1994, which was acontinuation-in-part of U.S. Patent Application No. 07/817,575, filed onJan. 7, 1992, now abandoned, the complete disclosures of which areincorporated herein by reference for all purposes.

The present application is also related to commonly assigned U.S. Pat.No. 5,697,882, filed Nov. 22, 1995, the complete disclosure of which isincorporated herein by reference for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to a medical apparatus having a distalcurved configuration which avoids contact of the apparatus distal endwith an introducer device. The present invention also relates to thefield of electrosurgery, and more particularly to surgical devices andmethods which employ high frequency electrical energy to treat tissue inregions of the spine. The present invention is particularly suited forthe treatment of the discs, cartilage, ligaments, and other tissuewithin the vertebral column.

The major causes of persistent, often disabling, back pain aredisruption of the disc annulus, chronic inflammation of the disc (e.g.,herniation), or relative instability of the vertebral bodies surroundinga given disc, such as the instability that often occurs due to astretching of the interspinous tissue surrounding the vertebrae.Intervertebral discs mainly function to cushion and tether thevertebrae, while the interspinous tissue (i.e., ligaments, tendons andcartilage, and the like) function to support the vertebrae so as toprovide flexibility and stability to the patient's spine.

Spinal discs comprise a central hydrophilic cushion, the nucleuspulposus, surrounded by a multi-layered fibrous ligament, the annulusfibrosus. As discs degenerate, they lose their water content and height,bringing the adjoining vertebrae closer together. This results in aweakening of the shock absorption properties of the disc and a narrowingof the nerve openings (foramen) in the sides of the spine which maypinch these nerves. This disc degeneration can eventually cause back andleg pain. Weakness in the annulus from degenerative discs or disc injurycan allow fragments of nucleus pulposus from within the disc space tomigrate through the annulus fibrosus and into the spinal canal. There,displaced nucleus or protrusion of annulus fibrosus, e.g., herniation,may impinge on spinal nerve roots. A weakening of the annulus fibrosuscan cause the disc to bulge, e.g., a contained herniation, and the mereproximity of the nucleus pulposus or the damaged annulus to a nerve cancause direct pressure against the nerve, resulting in pain and sensoryand motor deficit.

Often, inflammation from disc herniation can be treated successfully bynon-surgical means, such as rest, therapeutic exercise, oralanti-inflammatory medications or epidural injection of corticosteroids.Such treatments result in a gradual but progressive improvement insymptoms and allows the patient to avoid surgical intervention.

In some cases, the disc tissue is irreparably damaged, therebynecessitating removal of a portion of the disc or the entire disc toeliminate the source of inflammation and pressure. In more severe cases,the adjacent vertebral bodies must be stabilized following excision ofthe disc material to avoid recurrence of the disabling back pain. Oneapproach to stabilizing the vertebrae, termed spinal fusion, is toinsert an interbody graft or implant into the space vacated by thedegenerative disc. In this procedure, a small amount of bone may begrafted and packed into the implants. This allows the bone to growthrough and around the implant, fusing the vertebral bodies andpreventing reoccurrence of the symptoms.

Until recently, surgical spinal procedures resulted in major operationsand traumatic dissection of muscle and bone removal or bone fusion. Toovercome the disadvantages of traditional traumatic spine surgery,minimally invasive spine surgery was developed. In endoscopic spinalprocedures, the spinal canal is not violated and therefore epiduralbleeding with ensuing scarring is minimized or completely avoided. Inaddition, the risk of instability from ligament and bone removal isgenerally lower in endoscopic procedures than with open procedure.Further, more rapid rehabilitation facilitates faster recovery andreturn to work.

Minimally invasive techniques for the treatment of spinal diseases ordisorders include chemonucleolysis, laser techniques, and mechanicaltechniques. These procedures generally require the surgeon to form apassage or operating corridor from the external surface of the patientto the spinal disc(s) for passage of surgical instruments, implants andthe like. Typically, the formation of this operating corridor requiresthe removal of soft tissue, muscle or other types of tissue depending onthe procedure (i.e., laparascopic, thoracoscopic, arthroscopic, back,etc.). This tissue is usually removed with mechanical instruments, suchas pituitary rongeurs, curettes, graspers, cutters, drills,microdebriders and the like. Unfortunately, these mechanical instrumentsgreatly lengthen and increase the complexity of the procedure. Inaddition, these instruments might sever blood vessels within thistissue, usually causing profuse bleeding that obstructs the surgeon'sview of the target site.

Once the operating corridor is established, the nerve root is retractedand a portion or all of the disc is removed with mechanical instruments,such as a pituitary rongeur. In addition to the above problems withmechanical instruments, there are serious concerns because theseinstruments are not precise, and it is often difficult, during theprocedure, to differentiate between the target disc tissue, and otherstructures within the spine, such as bone, cartilage, ligaments, nervesand non-target tissue. Thus, the surgeon must be extremely careful tominimize damage to the cartilage and bone within the spine, and to avoiddamaging nerves, such as the spinal nerves and the dura matersurrounding the spinal cord.

Lasers were initially considered ideal for spine surgery because lasersablate or vaporize tissue with heat, which also acts to cauterize andseal the small blood vessels in the tissue. Unfortunately, lasers areboth expensive and somewhat tedious to use in these procedures. Anotherdisadvantage with lasers is the difficulty in judging the depth oftissue ablation. Since the surgeon generally points and shoots the laserwithout contacting the tissue, he or she does not receive any tactilefeedback to judge how deeply the laser is cutting. Because healthytissue, bones, ligaments and spinal nerves often lie within closeproximity of the spinal disc, it is essential to maintain a minimumdepth of tissue damage, which cannot always be ensured with a laser.

Monopolar and bipolar radiofrequency devices have been used in limitedroles in spine surgery, such as to cauterize severed vessels to improvevisualization. Monopolar devices, however, suffer from the disadvantagethat the electric current will flow through undefined paths in thepatient's body, thereby increasing the risk of undesirable electricalstimulation to portions of the patient's body. In addition, since thedefined path through the patient's body has a relatively high impedance(because of the large distance or resistivity of the patient's body),large voltage differences must typically be applied between the returnand active electrodes in order to generate a current suitable forablation or cutting of the target tissue. This current, however, mayinadvertently flow along body paths having less impedance than thedefined electrical path, which will substantially increase the currentflowing through these paths, possibly causing damage to or destroyingsurrounding tissue or neighboring peripheral nerves.

Other disadvantages of conventional RF devices, particularly monopolardevices, is nerve stimulation and interference with nerve monitoringequipment in the operating room. In addition, these devices typicallyoperate by creating a voltage difference between the active electrodeand the target tissue, causing an electrical arc to form across thephysical gap between the electrode and tissue. At the point of contactof the electric arcs with tissue, rapid tissue heating occurs due tohigh current density between the electrode and tissue. This high currentdensity causes cellular fluids to rapidly vaporize into steam, therebyproducing a “cutting effect” along the pathway of localized tissueheating. Thus, the tissue is parted along the pathway of evaporatedcellular fluid, inducing undesirable collateral tissue damage in regionssurrounding the target tissue site. This collateral tissue damage oftencauses indiscriminate destruction of tissue, resulting in the loss ofthe proper function of the tissue. In addition, the device does notremove any tissue directly, but rather depends on destroying a zone oftissue and allowing the body to eventually remove the destroyed tissue.

Many patients experience discogenic pain due to defects or disorders ofintervertebral discs. Such disc defects include annular fissures,fragmentation of the nucleus pulposus, and contained herniation. Acommon cause of pain related to various disc disorders is compression ofa nerve root by the disc. In many patients for whom major spinal surgeryis not indicated, discogenic pain naturally diminishes in severity overan extended period of time, perhaps several months. There is a need foran electrosurgical apparatus which is adapted for treating such patientsto alleviate the chronic, and often debilitating, pain associated withspinal nerve root compression. The instant invention provides apparatusfor decompressing nerve roots by ablation of disc tissue at relativelylow temperatures, wherein one or more channels are formed in the disc,the volume of the disc is decreased, and discogenic pain is alleviated.

There is also a need for an apparatus wherein a medical instrumenthaving one or more sensitive or fragile components can be advanced fromand retracted into a lumen of an introducer device while avoidingcontact between the sensitive or fragile component(s) and the introducerdevice. The instant invention provides such apparatus, as is describedin enabling detail hereinbelow.

SUMMARY OF THE INVENTION

The present invention provides systems, apparatus, and methods forselectively applying electrical energy to structures within a patient'sbody, such as the intervertebral disc. The systems and methods of thepresent invention are useful for shrinkage, ablation, resection,aspiration, and/or hemostasis of tissue and other body structures inopen and endoscopic spine surgery. In particular, the present inventionincludes a method and system for debulking, ablating, and shrinking thedisc.

The present invention further relates to an electrosurgical probeincluding an elongated shaft having first and second curves in thedistal end portion of the shaft, wherein the shaft can be rotated withinan intervertebral disc to contact fresh tissue of the nucleus pulposus.The present invention also relates to an electrosurgical probe includingan elongated shaft, wherein the shaft distal end can be guided to aspecific target site within a disc, and the shaft distal end is adaptedfor localized ablation of targeted disc tissue. The present inventionfurther relates to a probe having an elongated shaft, wherein the shaftincludes an active electrode, an insulating collar, and an outer shield,and wherein the active electrode includes a head having an apical spikeand a cusp. The present invention still further relates to a method forablating disc tissue with an electrosurgical probe, wherein the probeincludes an elongated shaft, and the shaft distal end is guided to aspecific target site within a disc.

In one aspect, the present invention provides a method of treating aherniated intervertebral disc. The method comprises positioning at leastone active electrode within the intervertebral disc. High frequencyvoltage is applied between the active electrode(s) and one or morereturn electrode(s) to debulk, ablate, coagulate and/or shrink at leasta portion of the nucleus pulposus and/or annulus. The high frequencyvoltage effects a controlled depth of thermal heating to reduce thewater content of the nucleus pulposus, thereby debulking the nucleuspulposus and reducing the internal pressure on the annulus fibrosus.

In an exemplary embodiment, an electrically conductive media, such asisotonic saline or an electrically conductive gel, is delivered to thetarget site within the intervertebral disc prior to delivery of the highfrequency energy. The conductive media will typically fill the entiretarget region such that the active electrode(s) are submerged throughoutthe procedure. In other embodiments, the extracellular conductive fluid(e.g., the nucleus pulposus) in the patient's disc may be used as asubstitute for, or as a supplement to, the electrically conductive mediathat is applied or delivered to the target site. For example, in someembodiments, an initial amount of conductive media is provided toinitiate the requisite conditions for ablation. After initiation, theconductive fluid already present in the patient's tissue is used tosustain these conditions.

In another aspect, the present invention provides a method of treating adisc having a contained herniation or fissure. The method comprisesintroducing an electrosurgical instrument into the patient'sintervertebral disc either percutaneously or through an open procedure.The instrument is steered or otherwise guided into close proximity tothe contained herniation or fissure and a high frequency voltage isapplied between an active electrode and a return electrode so as todebulk the nucleus pulposus adjacent to the contained herniation orfissure. In some embodiments a conductive fluid is delivered into theintervertebral disc prior to applying the high frequency voltage toensure that sufficient conductive fluid exists for plasma formation andto conduct electric current between the active and return electrodes.Alternatively, the conductive fluid can be delivered to the target siteduring the procedure. The heating delivered through the electricallyconductive fluid debulks the nucleus pulposus, and reduces the pressureon the annulus fibrosus so as to reduce the pressure on the affectednerve root and alleviate neck and back pain.

In another aspect, the present invention provides a method for treatingdegenerative intervertebral discs. The active electrode(s) are advancedinto the target disc tissue in an ablation mode, where the highfrequency voltage is sufficient to ablate or remove the nucleus pulposusthrough molecular dissociation or disintegration processes. In theseembodiments, the high frequency voltage applied to the activeelectrode(s) is sufficient to vaporize an electrically conductive fluid(e.g., gel, saline and/or intracellular fluid) between the activeelectrode(s) and the tissue. Within the vaporized fluid, a ionizedplasma is formed and charged particles (e.g., electrons) cause themolecular breakdown or disintegration of several cell layers of thenucleus pulposus. This molecular dissociation is accompanied by thevolumetric removal of the tissue. This process can be preciselycontrolled to effect the volumetric removal of tissue as thin as 10microns to 150 microns with minimal heating of, or damage to,surrounding or underlying tissue structures. A more complete descriptionof this phenomena is described in commonly assigned U.S. Pat. No.5,697,882 the complete disclosure of which is incorporated herein byreference.

An apparatus according to the present invention generally includes ashaft having proximal and distal end portions, an active electrode atthe distal end and one or more connectors for coupling the activeelectrode to a source of high frequency electrical energy. The probe orcatheter may assume a wide variety of configurations, with the primarypurpose being to introduce the electrode assembly into the patient'sdisc (in an open or endoscopic procedure) and to permit the treatingphysician to manipulate the electrode assembly from a proximal end ofthe shaft. The probe shafts can be flexible, curved, or steerable so asto allow the treating physician to move the active electrode into closeproximity of the herniation. The electrode assembly includes one or moreactive electrode(s) and a return electrode spaced from the activeelectrode(s) either on the instrument shaft or separate from theinstrument shaft.

The active electrode(s) may comprise a single active electrode, or anelectrode array, extending from an electrically insulating supportmember, typically made of an inorganic material such as ceramic,silicone or glass. The active electrode will usually have a smallerexposed surface area than the return such that the current densities aremuch higher at the active electrode than at the return electrode.Preferably, the return electrode has a relatively large, smooth surfacesextending around the instrument shaft to reduce current densities,thereby minimizing damage to adjacent tissue.

In another aspect of the invention there is provided a medical apparatusincluding a shaft distal end portion, a first curve and a second curveproximal to the first curve, wherein the first curve is in a firstdirection and the second curve is in a direction opposite to the firstdirection. In one embodiment, the medical apparatus further includes anintroducer device having a lumen adapted for passing the shaft distalend portion therethrough. In one aspect of the invention, the tip orterminus of the shaft distal end portion remains substantially centrallylocated within the lumen when the shaft distal end portion is passedwithin the lumen and when the distal tip is advanced from and retractedinto the distal end of the introducer device. The transverse location ofthe shaft distal tip within the lumen is determined by the angle of thefirst curve and by the length of a portion of the shaft distal to thefirst curve. The angle of the second curve determines the degree ofdeflection of the shaft distal tip away from the longitudinal axis ofthe shaft when the shaft is free from the introducer device.

In another aspect of the invention, an apparatus for performingelectrosurgery generally includes a shaft including a shaft distal endportion, a shaft proximal end portion, and at least one active electrodedisposed on the shaft distal end portion, wherein the shaft distal endportion has curvature proximal to the at least one active electrode. Inone embodiment, the curvature of the shaft includes a first curve and asecond curve proximal to the first curve. The first curve and the secondcurve are preferably in the same plane relative to the longitudinal axisof the shaft, and the first curve and the second curve are in differentdirections relative to the longitudinal axis of the shaft. In oneembodiment, an angle of the second curve is greater than an angle of thefirst curve. In another embodiment, the shaft is adapted for ablation oftissue, and the shaft has a specific curvature which is defined in theapparatus at the time of manufacture and the specific curvature issubstantially retained in use, i.e. during ablation of tissue by theapparatus. In another embodiment, the at least one active electrodeincludes an apical spike and a substantially equatorial cusp. The atleast one active electrode preferably promotes high current density andgeneration of a plasma in the presence of an electrically conductivefluid and an applied high frequency voltage.

In another embodiment, the shaft includes a filament connected to anelectrode head, a first insulating sleeve on the filament, asubstantially cylindrical return electrode on the first sleeve, a secondinsulating sleeve on the return electrode, and a shield on the secondsleeve. The first sleeve preferably has an insulating collar, comprisinga glass, ceramic, or silicone rubber material, disposed on a distal endthereof. The shaft may further include one or more of: a distal trackingdevice, one or more depth markings, and a substantially proximalmechanical stop.

In another embodiment, the invention provides an electrosurgical probeand introducer needle combination for treating an intervertebral disc,wherein the combination includes a probe including a shaft having ashaft distal end, at least one active electrode, and at least one returnelectrode. In one embodiment the shaft distal end further includes afirst curve and a second curve proximal to the first curve. Thecombination further includes an introducer needle having a lumen and aneedle distal end. The introducer needle is adapted for passing theshaft distal end through the lumen, and for guiding the shaft distal enddistally beyond the needle distal end. Accordingly, the shaft distal endmay be guided towards and into an intervertebral disc. Theelectrosurgical probe of the combination may generally include thoseelements and features described hereinabove, including an electrode headhaving an apical spike, an insulating collar, and a shield. The lumen ofthe introducer needle preferably has a diameter in the range of fromabout 105% to about 500% of the diameter of the shaft distal end.

In another aspect, the invention provides a method of making anelectrosurgical apparatus, wherein the method involves providing a shafthaving at least one curve therein, providing a handle, and affixing thehandle to the curved shaft. In one embodiment, providing a shaft for usein manufacture of the apparatus involves: providing an active electrodehaving a filament and a spiked head, and encasing the filamentsequentially within at least one of a first insulating sleeve, a returnelectrode, a second insulating sleeve, and a shield. In one embodiment,the method involves forming a first curve and a second curve in theshaft, wherein the first curve is introduced prior to introduction ofthe second curve.

For a further understanding of the nature and advantages of theinvention, reference should be made to the following description takenin conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an electrosurgical system incorporatinga power supply and an electrosurgical probe for tissue ablation,resection, incision, contraction and for vessel hemostasis according tothe present invention;

FIG. 2 schematically illustrates one embodiment of a power supplyaccording to the present invention;

FIG. 3 illustrates an electrosurgical system incorporating a pluralityof active electrodes and associated current limiting elements;

FIG. 4 is a side view of an electrosurgical probe according to thepresent invention;

FIG. 5 is a view of the distal end portion of the probe of FIG. 2

FIG. 6 is an exploded view of a proximal portion of the electrosurgicalprobe;

FIGS. 7A and 7B are perspective and end views, respectively, of analternative electrosurgical probe incorporating an inner fluid lumen;

FIGS. 8A–8C are cross-sectional views of the distal portions of threedifferent embodiments of an electrosurgical probe according to thepresent invention;

FIGS. 9–12 are end views of alternative embodiments of the probe of FIG.4, incorporating aspiration electrode(s);

FIG. 13 is a side view of the distal portion of the shaft of anelectrosurgical probe, according to one embodiment of the invention;

FIGS. 14A–14C illustrate an alternative embodiment incorporating ascreen electrode;

FIGS. 15A–15D illustrate four embodiments of electrosurgical probesspecifically designed for treating spinal defects;

FIG. 16 illustrates an electrosurgical system incorporating a dispersivereturn pad for monopolar and/or bipolar operations;

FIG. 17 illustrates a catheter system for electrosurgical treatment ofintervertebral discs according to the present invention;

FIGS. 18–22 illustrate a method of performing a microendoscopicdiscectomy according to the principles of the present invention;

FIGS. 23–25 illustrates another method of treating a spinal disc withone of the catheters or probes of the present invention;

FIG. 26A is a side view of an electrosurgical probe according to theinvention;

FIG. 26B is a side view of the distal end portion of the electrosurgicalprobe of FIG. 26A;

FIG. 27A is a side view of an electrosurgical probe having a curvedshaft;

FIG. 27B is a side view of the distal end portion of the curved shaft ofFIG. 27A, with the shaft distal end portion within an introducer device;

FIG. 27C is a side view of the distal end portion of the curved shaft ofFIG. 27B in the absence of the introducer device;

FIG. 28A is a side view of the distal end portion of an electrosurgicalprobe showing an active electrode having an apical spike and anequatorial cusp;

FIG. 28B is a cross-sectional view of the distal end portion of theelectrosurgical probe of FIG. 28A;

FIG. 29 is a side view of the distal end portion a shaft of anelectrosurgical probe, indicating the position of a first curve and asecond curve in relation to the head of the active electrode;

FIG. 30A shows the distal end portion of the shaft of an electrosurgicalprobe extended distally from an introducer needle;

FIG. 30B illustrates the position of the active electrode in relation tothe inner wall of the introducer needle upon retraction of the activeelectrode within the introducer needle;

FIGS. 31A, 31B show a side view and an end view, respectively, of acurved shaft of an electrosurgical probe, in relation to an introducerneedle;

FIG. 32A shows the proximal end portion of the shaft of anelectrosurgical probe, wherein the shaft includes a plurality of depthmarkings;

FIG. 32B shows the proximal end portion of the shaft of anelectrosurgical probe, wherein the shaft includes a mechanical stop;

FIG. 33 illustrates stages in manufacture of an active electrode of anelectrosurgical probe of the present invention;

FIG. 34 schematically represents a series of steps involved in a methodof making a probe shaft of the present invention;

FIG. 35 schematically represents a series of steps involved in a methodof making an electrosurgical probe of the present invention;

FIG. 36A schematically represents a normal intervertebral disc inrelation to the spinal cord;

FIG. 36B schematically represents an intervertebral disc exhibiting aprotrusion of the nucleus pulposus and a concomitant distortion of theannulus fibrosus;

FIG. 36C schematically represents an intervertebral disc exhibiting aplurality of fissures within the annulus fibrosus and a concomitantdistortion of the annulus fibrosus;

FIG. 36D schematically represents an intervertebral disc exhibitingfragmentation of the nucleus pulposus and a concomitant distortion ofthe annulus fibrosus;

FIG. 37 schematically represents translation of a curved shaft of anelectrosurgical probe within the nucleus pulposus for treatment of anintervertebral disc;

FIG. 38 shows a shaft of an electrosurgical probe within anintervertebral disc, wherein the shaft distal end is targeted to aspecific site within the disc;

FIG. 39 schematically represents a series of steps involved in a methodof ablating disc tissue according to the present invention;

FIG. 40 schematically represents a series of steps involved in a methodof guiding an electrosurgical probe to a target site within anintervertebral disc for ablation of targeted disc tissue, according toanother embodiment of the invention;

FIG. 41 shows treatment of an intervertebral disc using anelectrosurgical probe and a separately introduced ancillary device,according to another embodiment of the invention;

FIG. 42 is a side view of an electrosurgical probe having a trackingdevice;

FIG. 43A shows a steerable electrosurgical probe wherein the shaft ofthe probe assumes a substantially linear configuration;

FIG. 43B shows the steerable electrosurgical probe of FIG. 44A, whereinthe shaft distal end of the probe adopts a bent configuration; and

FIG. 44 shows a steerable electrosurgical probe and an ancillary deviceinserted within the nucleus pulposus of an intervertebral disc.

DESCRIPTION OF SPECIFIC EMBODIMENTS

The present invention provides systems and methods for selectivelyapplying electrical energy to a target location within or on a patient'sbody, particularly including support tissue or other body structures inthe spine. These procedures include treating interspinous tissue,degenerative discs, laminectomy/discectomy procedures for treatingherniated discs, decompressive laminectomy for stenosis in thelumbosacral and cervical spine, localized tears or fissures in theannulus, nucleotomy, disc fusion procedures, medial facetectomy,posterior lumbosacral and cervical spine fusions, treatment of scoliosisassociated with vertebral disease, foraminotomies to remove the roof ofthe intervertebral foramina to relieve nerve root compression andanterior cervical and lumbar discectomies. These procedures may beperformed through open procedures, or using minimally invasivetechniques, such as thoracoscopy, arthroscopy, laparascopy or the like.

The present invention involves techniques for treating discabnormalities with RF energy. In some embodiments, RF energy is used toablate, debulk and/or stiffen the tissue structure of the disc to reducethe volume of the disc, thereby relieving neck and back pain. In oneaspect of the invention, spinal disc tissue is volumetrically removed orablated to form holes, channels, divots or other spaces within the disc.In this procedure, a high frequency voltage difference is appliedbetween one or more active electrode(s) and one or more returnelectrode(s) to develop high electric field intensities in the vicinityof the target tissue. The high electric field intensities adjacent theactive electrode(s) lead to electric field induced molecular breakdownof target tissue through molecular dissociation (rather than thermalevaporation or carbonization). Applicant believes that the tissuestructure is volumetrically removed through molecular disintegration oflarger organic molecules into smaller molecules and/or atoms, such ashydrogen, oxygen, oxides of carbon, hydrocarbons and nitrogen compounds.This molecular disintegration completely removes the tissue structure,as opposed to dehydrating the tissue material by the removal of liquidwithin the cells of the tissue and extracellular fluids, as is typicallythe case with electrosurgical desiccation and vaporization.

The present invention also involves a system and method for treating theinterspinous tissue (e.g., tendons, cartilage, synovial tissue inbetween the vertebrae, and other support tissue within and surroundingthe vertebral column). In some embodiments, RF energy is used to heatand shrink the interspinous tissue to stabilize the vertebral column andreduce pain in the back and neck. In one aspect of the invention, anactive electrode is positioned adjacent the interspinous tissue and theinterspinous tissue is heated, preferably with RF energy, to asufficient temperature to shrink the interspinous tissue. In a specificembodiment, a high frequency voltage difference is applied between oneor more active electrode(s) and one or more return electrode(s) todevelop high electric field intensities in the vicinity of the targettissue to controllably heat the target tissue.

The high electric field intensities may be generated by applying a highfrequency voltage that is sufficient to vaporize an electricallyconductive fluid over at least a portion of the active electrode(s) inthe region between the distal tip of the active electrode(s) and thetarget tissue. The electrically conductive fluid may be a liquid or gas,such as isotonic saline, blood, extracelluar or intracellular fluid,delivered to, or already present at, the target site, or a viscousfluid, such as a gel, applied to the target site. Since the vapor layeror vaporized region has a relatively high electrical impedance, itminimizes the current flow into the electrically conductive fluid. Thisionization, under the conditions described herein, induces the dischargeof energetic electrons and photons from the vapor layer and to thesurface of the target tissue A more detailed description of thisphenomena, termed Coblation® can be found in commonly assigned U.S. Pat.No. 5,697,882 the complete disclosure of which is incorporated herein byreference.

Applicant believes that the principle mechanism of tissue removal in theCoblation® mechanism of the present invention is energetic electrons orions that have been energized in a plasma adjacent to the activeelectrode(s). When a liquid is heated enough that atoms vaporize off thesurface faster than they recondense, a gas is formed. When the gas isheated enough that the atoms collide with each other and knock theirelectrons off in the process, an ionized gas or plasma is formed (theso-called “fourth state of matter”). A more complete description ofplasma can be found in Plasma Physics, by R. J. Goldston and P. H.Rutherford of the Plasma Physics Laboratory of Princeton University(1995), the complete disclosure of which is incorporated herein byreference. When the density of the vapor layer (or within a bubbleformed in the electrically conducting liquid) becomes sufficiently low(i.e., less than approximately 10²⁰ atoms/cm³ for aqueous solutions),the electron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Once the ionic particles in the plasmalayer have sufficient energy, they accelerate towards the target tissue.Energy evolved by the energetic electrons (e.g., 3.5 eV to 5 eV) cansubsequently bombard a molecule and break its bonds, dissociating amolecule into free radicals, which then combine into final gaseous orliquid species.

Plasmas may be formed by heating a gas and ionizing the gas by drivingan electric current through it, or by shining radio waves into the gas.Generally, these methods of plasma formation give energy to freeelectrons in the plasma directly, and then electron-atom collisionsliberate more electrons, and the process cascades until the desireddegree of ionization is achieved. Often, the electrons carry theelectrical current or absorb the radio waves and, therefore, are hotterthan the ions. Thus, in applicant's invention, the electrons, which arecarried away from the tissue towards the return electrode, carry most ofthe plasma's heat with them, allowing the ions to break apart the tissuemolecules in a substantially non-thermal manner.

In some embodiments, the present invention applies high frequency (RF)electrical energy in an electrically conducting media environment toshrink or remove (i.e., resect, cut, or ablate) a tissue structure andto seal transected vessels within the region of the target tissue. Thepresent invention may also be useful for sealing larger arterialvessels, e.g., on the order of about 1 mm in diameter. In someembodiments, a high frequency power supply is provided having anablation mode, wherein a first voltage is applied to an active electrodesufficient to effect molecular dissociation or disintegration of thetissue, and a coagulation mode, wherein a second, lower voltage isapplied to an active electrode (either the same or a differentelectrode) sufficient to heat, shrink, and/or achieve hemostasis ofsevered vessels within the tissue. In other embodiments, anelectrosurgical instrument is provided having one or more coagulationelectrode(s) configured for sealing a severed vessel, such as anarterial vessel, and one or more active electrodes configured for eithercontracting the collagen fibers within the tissue or removing (ablating)the tissue, e.g., by applying sufficient energy to the tissue to effectmolecular dissociation. In the latter embodiments, the coagulationelectrode(s) may be configured such that a single voltage can be appliedto coagulate with the coagulation electrode(s), and to ablate or shrinkwith the active electrode(s). In other embodiments, the power supply iscombined with the coagulation instrument such that the coagulationelectrode is used when the power supply is in the coagulation mode (lowvoltage), and the active electrode(s) are used when the power supply isin the ablation mode (higher voltage).

In one method of the present invention, one or more active electrodesare brought into close proximity to tissue at a target site, and thepower supply is activated in the ablation mode such that sufficientvoltage is applied between the active electrodes and the returnelectrode to volumetrically remove the tissue through moleculardissociation, as described below. During this process, vessels withinthe tissue will be severed. Smaller vessels will be automatically sealedwith the system and method of the present invention. Larger vessels, andthose with a higher flow rate, such as arterial vessels, may not beautomatically sealed in the ablation mode. In these cases, the severedvessels may be sealed by activating a control (e.g., a foot pedal) toreduce the voltage of the power supply into the coagulation mode. Inthis mode, the active electrodes may be pressed against the severedvessel to provide sealing and/or coagulation of the vessel.Alternatively, a coagulation electrode located on the same or adifferent instrument may be pressed against the severed vessel. Once thevessel is adequately sealed, the surgeon activates a control (e.g.,another foot pedal) to increase the voltage of the power supply backinto the ablation mode.

In another aspect, the present invention may be used to shrink orcontract collagen connective tissue which support the vertebral columnor connective tissue within the disc. In these procedures, the RF energyheats the tissue directly by virtue of the electrical current flowtherethrough, and/or indirectly through the exposure of the tissue tofluid heated by RF energy, to elevate the tissue temperature from normalbody temperatures (e.g., 37° C.) to temperatures in the range of 45° C.to 90° C., preferably in the range from about 60° C. to 70° C. Thermalshrinkage of collagen fibers occurs within a small temperature rangewhich, for mammalian collagen is in the range from 60° C. to 70° C.(Deak, G., et al., “The Thermal Shrinkage Process of Collagen Fibres asRevealed by Polarization Optical Analysis of Topooptical StainingReactions,” Acta Morphological Acad. Sci. of Hungary, Vol. 15(2), pp.195–208, 1967). Collagen fibers typically undergo thermal shrinkage inthe range of 60° C. to about 70° C. Previously reported research hasattributed thermal shrinkage of collagen to the cleaving of the internalstabilizing cross-linkages within the collagen matrix (Deak, ibid). Ithas also been reported that when the collagen temperature is increasedabove 70° C., the collagen matrix begins to relax again and theshrinkage effect is reversed resulting in no net shrinkage (Allain, J.C., et al., “Isometric Tensions Developed During the HydrothermalSwelling of Rat Skin,” Connective Tissue Research, Vol. 7, pp 127–133,1980), the complete disclosure of which is incorporated by reference.Consequently, the controlled heating of tissue to a precise depth iscritical to the achievement of therapeutic collagen shrinkage. A moredetailed description of collagen shrinkage can be found in U.S. patentapplication Ser. No. 08/942,580 filed on Oct. 2, 1997, the completedisclosure of which is incorporated by reference.

The preferred depth of heating to effect the shrinkage of collagen inthe heated region (i.e., the depth to which the tissue is elevated totemperatures between 60° C. to 70° C.) generally depends on (1) thethickness of the target tissue, (2) the location of nearby structures(e.g., nerves) that should not be exposed to damaging temperatures,and/or (3) the location of the collagen tissue layer within whichtherapeutic shrinkage is to be effected. The depth of heating is usuallyin the range from 1.0 mm to 5.0 mm. In some embodiments of the presentinvention, the tissue is purposely damaged in a thermal heating mode tocreate necrosed or scarred tissue at the tissue surface. The highfrequency voltage in the thermal heating mode is below the threshold ofablation as described above, but sufficient to cause some thermal damageto the tissue immediately surrounding the electrodes without vaporizingor otherwise debulking this tissue in situ. Typically, it is desired toachieve a tissue temperature in the range of about 60° C. to 100° C. toa depth of about 0.2 mm to 5 mm, usually about 1 mm to 2 mm. The voltagerequired for this thermal damage will partly depend on the electrodeconfigurations, the conductivity of the area immediately surrounding theelectrodes, the time period in which the voltage is applied and thedepth of tissue damage desired. With the electrode configurationsdescribed in this application (e.g., FIGS. 15A–15D), the voltage levelfor thermal heating will usually be in the range of about 20 volts rmsto 300 volts rms, preferably about 60 volts rms to 200 volts rms. Thepeak-to-peak voltages for thermal heating with a square wave form havinga crest factor of about 2 are typically in the range of about 40 voltspeak-to-peak to 600 volts peak-to-peak, preferably about 120 voltspeak-to-peak to 400 volts peak-to-peak. In some embodiments, capacitorsor other electrical elements may be used to increase the crest factor upto 10. The higher the voltage is within this range, the less timerequired. If the voltage is too high, however, the surface tissue may bevaporized, debulked or ablated, which is generally undesirable.

In yet another embodiment, the present invention may be used fortreating degenerative discs with fissures or tears. In theseembodiments, the active and return electrode(s) are positioned in oraround the inner wall of the disc annulus such that the active electrodeis adjacent to the fissure. High frequency voltage is applied betweenthe active and return electrodes to heat the fissure and shrink thecollagen fibers and create a seal or weld within the inner wall, therebyhelping to close the fissure in the annulus. In these embodiments, thereturn electrode will typically be positioned proximally from the activeelectrode(s) on the instrument shaft, and an electrically conductivefluid will be applied to the target site to create the necessary currentpath between the active and return electrodes. In alternativeembodiments, the disc tissue may complete this electrically conductivepath.

The present invention is also useful for removing or ablating tissuearound nerves, such as spinal, peripheral or cranial nerves. One of thesignificant drawbacks with the prior art shavers or microdebriders,conventional electrosurgical devices and lasers is that these devices donot differentiate between the target tissue and the surrounding nervesor bone. Therefore, the surgeon must be extremely careful during theseprocedures to avoid damage to the bone or nerves within and around thetarget site. In the present invention, the Coblation® process forremoving tissue results in extremely small depths of collateral tissuedamage as discussed above. This allows the surgeon to remove tissueclose to a nerve without causing collateral damage to the nerve fibers.

In addition to the generally precise nature of the novel mechanisms ofthe present invention, applicant has discovered an additional method ofensuring that adjacent nerves are not damaged during tissue removal.According to the present invention, systems and methods are provided fordistinguishing between the fatty tissue immediately surrounding nervefibers and the normal tissue that is to be removed during the procedure.Peripheral nerves usually comprise a connective tissue sheath, orepineurium, enclosing the bundles of nerve fibers, each bundle beingsurrounded by its own sheath of connective tissue (the perineurium) toprotect these nerve fibers. The outer protective tissue sheath orepineurium typically comprises a fatty tissue (e.g., adipose tissue)having substantially different electrical properties than the normaltarget tissue, such as the turbinates, polyps, mucus tissue or the like,that are, for example, removed from the nose during sinus procedures.The system of the present invention measures the electrical propertiesof the tissue at the tip of the probe with one or more activeelectrode(s). These electrical properties may include electricalconductivity at one, several or a range of frequencies (e.g., in therange from 1 kHz to 100 MHz), dielectric constant, capacitance orcombinations of these. In this embodiment, an audible signal may beproduced when the sensing electrode(s) at the tip of the probe detectsthe fatty tissue surrounding a nerve, or direct feedback control can beprovided to only supply power to the active electrode(s) eitherindividually or to the complete array of electrodes, if and when thetissue encountered at the tip or working end of the probe is normaltissue based on the measured electrical properties.

In one embodiment, the current limiting elements (discussed in detailabove) are configured such that the active electrodes will shut down orturn off when the electrical impedance reaches a threshold level. Whenthis threshold level is set to the impedance of the fatty tissuesurrounding nerves, the active electrodes will shut off whenever theycome in contact with, or in close proximity to, nerves. Meanwhile, theother active electrodes, which are in contact with or in close proximityto tissue, will continue to conduct electric current to the returnelectrode. This selective ablation or removal of lower impedance tissuein combination with the Coblation® mechanism of the present inventionallows the surgeon to precisely remove tissue around nerves or bone.Applicant has found that the present invention is capable ofvolumetrically removing tissue closely adjacent to nerves withoutimpairment the function of the nerves, and without significantlydamaging the tissue of the epineurium. One of the significant drawbackswith the prior art microdebriders, conventional electrosurgical devicesand lasers is that these devices do not differentiate between the targettissue and the surrounding nerves or bone. Therefore, the surgeon mustbe extremely careful during these procedures to avoid damage to the boneor nerves within and around the nasal cavity. In the present invention,the Coblation® process for removing tissue results in extremely smalldepths of collateral tissue damage as discussed above. This allows thesurgeon to remove tissue close to a nerve without causing collateraldamage to the nerve fibers.

In addition to the above, applicant has discovered that the Coblation®mechanism of the present invention can be manipulated to ablate orremove certain tissue structures, while having little effect on othertissue structures. As discussed above, the present invention uses atechnique of vaporizing electrically conductive fluid to form a plasmalayer or pocket around the active electrode(s), and then inducing thedischarge of energy from this plasma or vapor layer to break themolecular bonds of the tissue structure. Based on initial experiments,applicants believe that the free electrons within the ionized vaporlayer are accelerated in the high electric fields near the electrodetip(s). When the density of the vapor layer (or within a bubble formedin the electrically conducting liquid) becomes sufficiently low (i.e.,less than approximately 10²⁰ atoms/cm³ for aqueous solutions), theelectron mean free path increases to enable subsequently injectedelectrons to cause impact ionization within these regions of low density(i.e., vapor layers or bubbles). Energy evolved by the energeticelectrons (e.g., 4 eV to 5 eV) can subsequently bombard a molecule andbreak its bonds, dissociating a molecule into free radicals, which thencombine into final gaseous or liquid species.

The energy evolved by the energetic electrons may be varied by adjustinga variety of factors, such as: the number of active electrodes;electrode size and spacing; electrode surface area; asperities and sharpedges on the electrode surfaces; electrode materials; applied voltageand power; current limiting means, such as inductors; electricalconductivity of the fluid in contact with the electrodes; density of thefluid; and other factors. Accordingly, these factors can be manipulatedto control the energy level of the excited electrons. Since differenttissue structures have different molecular bonds, the present inventioncan be configured to break the molecular bonds of certain tissue, whilehaving too low an energy to break the molecular bonds of other tissue.For example, fatty tissue, (e.g., adipose) tissue has double bonds thatrequire a substantially higher energy level than 4 eV to 5 eV to break(typically on the order of about 8 eV). Accordingly, the presentinvention in its current configuration generally does not ablate orremove such fatty tissue. However, the present invention may be used toeffectively ablate cells to release the inner fat content in a liquidform. Of course, factors may be changed such that these double bonds canalso be broken in a similar fashion as the single bonds (e.g.,increasing voltage or changing the electrode configuration to increasethe current density at the electrode tips). A more complete descriptionof this phenomena can be found in co-pending U.S. patent applicationSer. No. 09/032,375, filed Feb. 27, 1998, the complete disclosure ofwhich is incorporated herein by reference.

In yet other embodiments, the present invention provides systems,apparatus and methods for selectively removing tumors, e.g., facialtumors, or other undesirable body structures while minimizing the spreadof viable cells from the tumor. Conventional techniques for removingsuch tumors generally result in the production of smoke in the surgicalsetting, termed an electrosurgical or laser plume, which can spreadintact, viable bacterial or viral particles from the tumor or lesion tothe surgical team or to other portions of the patient's body. Thispotential spread of viable cells or particles has resulted in increasedconcerns over the proliferation of certain debilitating and fataldiseases, such as hepatitis, herpes, HIV and papillomavirus. In thepresent invention, high frequency voltage is applied between the activeelectrode(s) and one or more return electrode(s) to volumetricallyremove at least a portion of the tissue cells in the tumor through thedissociation or disintegration of organic molecules into non-viableatoms and molecules. Specifically, the present invention converts thesolid tissue cells into non-condensable gases that are no longer intactor viable, and thus, not capable of spreading viable tumor particles toother portions of the patient's brain or to the surgical staff. The highfrequency voltage is preferably selected to effect controlled removal ofthese tissue cells while minimizing substantial tissue necrosis tosurrounding or underlying tissue. A more complete description of thisphenomena can be found in co-pending U.S. patent application Ser. No.09/109,219, filed Jun. 30, 1998, the complete disclosure of which isincorporated herein by reference.

The electrosurgical probe or catheter of the present invention cancomprise a shaft or a handpiece having a proximal end and a distal endwhich supports one or more active electrode(s). The shaft or handpiecemay assume a wide variety of configurations, with the primary purposebeing to mechanically support the active electrode and permit thetreating physician to manipulate the electrode from a proximal end ofthe shaft. The shaft may be rigid or flexible, with flexible shaftsoptionally being combined with a generally rigid external tube formechanical support. Flexible shafts may be combined with pull wires,shape memory actuators, and other known mechanisms for effectingselective deflection of the distal end of the shaft to facilitatepositioning of the electrode array. The shaft will usually include aplurality of wires or other conductive elements running axiallytherethrough to permit connection of the electrode array to a connectorat the proximal end of the shaft.

For endoscopic procedures within the spine, the shaft will have asuitable diameter and length to allow the surgeon to reach the targetsite (e.g., a disc or vertebra) by delivering the shaft through thethoracic cavity, the abdomen or the like. Thus, the shaft will usuallyhave a length in the range of about 5.0 cm to 30.0 cm, and a diameter inthe range of about 0.2 mm to about 20 mm. Alternatively, the shaft maybe delivered directly through the patient's back in a posteriorapproach, which would considerably reduce the required length of theshaft. In any of these embodiments, the shaft may also be introducedthrough rigid or flexible endoscopes. Alternatively, the shaft may be aflexible catheter that is introduced through a percutaneous penetrationin the patient. Specific shaft designs will be described in detail inconnection with the figures hereinafter.

In an alternative embodiment, the probe may comprise a long, thin needle(e.g., on the order of about 1 mm in diameter or less) that can bepercutaneously introduced through the patient's back directly into thespine. The needle will include one or more active electrode(s) forapplying electrical energy to tissues within the spine. The needle mayinclude one or more return electrode(s), or the return electrode may bepositioned on the patient's back, as a dispersive pad. In eitherembodiment, sufficient electrical energy is applied through the needleto the active electrode(s) to either shrink the collagen fibers withinthe spinal disc, to ablate tissue within the disc, or to shrink supportfibers surrounding the vertebrae.

The electrosurgical instrument may also be a catheter that is deliveredpercutaneously and/or endoluminally into the patient by insertionthrough a conventional or specialized guide catheter, or the inventionmay include a catheter having an active electrode or electrode arrayintegral with its distal end. The catheter shaft may be rigid orflexible, with flexible shafts optionally being combined with agenerally rigid external tube for mechanical support. Flexible shaftsmay be combined with pull wires, shape memory actuators, and other knownmechanisms for effecting selective deflection of the distal end of theshaft to facilitate positioning of the electrode or electrode array. Thecatheter shaft will usually include a plurality of wires or otherconductive elements running axially therethrough to permit connection ofthe electrode or electrode array and the return electrode to a connectorat the proximal end of the catheter shaft. The catheter shaft mayinclude a guide wire for guiding the catheter to the target site, or thecatheter may comprise a steerable guide catheter. The catheter may alsoinclude a substantially rigid distal end portion to increase the torquecontrol of the distal end portion as the catheter is advanced furtherinto the patient's body. Specific shaft designs will be described indetail in connection with the figures hereinafter.

The active electrode(s) are preferably supported within or by aninorganic insulating support positioned near the distal end of theinstrument shaft. The return electrode may be located on the instrumentshaft, on another instrument or on the external surface of the patient(i.e., a dispersive pad). The close proximity of nerves and othersensitive tissue in and around the spinal cord, however, makes a bipolardesign more preferable because this minimizes the current flow throughnon-target tissue and surrounding nerves. Accordingly, the returnelectrode is preferably either integrated with the instrument body, oranother instrument located in close proximity thereto. The proximal endof the instrument(s) will include the appropriate electrical connectionsfor coupling the return electrode(s) and the active electrode(s) to ahigh frequency power supply, such as an electrosurgical generator.

In some embodiments, the active electrode(s) have an active portion orsurface with surface geometries shaped to promote the electric fieldintensity and associated current density along the leading edges of theelectrodes. Suitable surface geometries may be obtained by creatingelectrode shapes that include preferential sharp edges, or by creatingasperities or other surface roughness on the active surface(s) of theelectrodes. Electrode shapes according to the present invention caninclude the use of formed wire (e.g., by drawing round wire through ashaping die) to form electrodes with a variety of cross-sectionalshapes, such as square, rectangular, L or V shaped, or the like.Electrode edges may also be created by removing a portion of theelongate metal electrode to reshape the cross-section. For example,material can be ground along the length of a round or hollow wireelectrode to form D or C shaped wires, respectively, with edges facingin the cutting direction. Alternatively, material can be removed atclosely spaced intervals along the electrode length to form transversegrooves, slots, threads or the like along the electrodes.

Additionally or alternatively, the active electrode surface(s) may bemodified through chemical, electrochemical or abrasive methods to createa multiplicity of surface asperities on the electrode surface. Thesesurface asperities will promote high electric field intensities betweenthe active electrode surface(s) and the target tissue to facilitateablation or cutting of the tissue. For example, surface asperities maybe created by etching the active electrodes with etchants having a pHless than 7.0 or by using a high velocity stream of abrasive particles(e.g., grit blasting) to create asperities on the surface of anelongated electrode. A more detailed description of such electrodeconfigurations can be found in U.S. Pat. No. 5,843,019, the completedisclosure of which is incorporated herein by reference.

The return electrode is typically spaced proximally from the activeelectrode(s) a suitable distance to avoid electrical shorting betweenthe active and return electrodes in the presence of electricallyconductive fluid. In most of the embodiments described herein, thedistal edge of the exposed surface of the return electrode is spacedabout 0.5 mm to 25 mm from the proximal edge of the exposed surface ofthe active electrode(s), preferably about 1.0 mm to 5.0 mm. Of course,this distance may vary with different voltage ranges, conductive fluids,and depending on the proximity of tissue structures to active and returnelectrodes. The return electrode will typically have an exposed lengthin the range of about 1 mm to 20 mm.

The current flow path between the active electrodes and the returnelectrode(s) may be generated by submerging the tissue site in anelectrical conducting fluid (e.g., within a viscous fluid, such as anelectrically conductive gel) or by directing an electrically conductivefluid along a fluid path to the target site (i.e., a liquid, such asisotonic saline, hypotonic saline or a gas, such as argon). Theconductive gel may also be delivered to the target site to achieve aslower more controlled delivery rate of conductive fluid. In addition,the viscous nature of the gel may allow the surgeon to more easilycontain the gel around the target site (e.g., rather than attempting tocontain isotonic saline). A more complete description of an exemplarymethod of directing electrically conductive fluid between the active andreturn electrodes is described in U.S. Pat. No. 5,697,281, previouslyincorporated herein by reference. Alternatively, the body's naturalconductive fluids, such as blood or extracellular saline, may besufficient to establish a conductive path between the returnelectrode(s) and the active electrode(s), and to provide the conditionsfor establishing a vapor layer, as described above. However, conductivefluid that is introduced into the patient is generally preferred overblood because blood will tend to coagulate at certain temperatures. Inaddition, the patient's blood may not have sufficient electricalconductivity to adequately form a plasma in some applications.Advantageously, a liquid electrically conductive fluid (e.g., isotonicsaline) may be used to concurrently “bathe” the target tissue surface toprovide an additional means for removing any tissue, and to cool theregion of the target tissue ablated in the previous moment.

The power supply, or generator, may include a fluid interlock forinterrupting power to the active electrode(s) when there is insufficientconductive fluid around the active electrode(s). This ensures that theinstrument will not be activated when conductive fluid is not present,minimizing the tissue damage that may otherwise occur. A more completedescription of such a fluid interlock can be found in commonly assigned,co-pending U.S. application Ser. No. 09/058,336, filed Apr. 10, 1998,the complete disclosure of which is incorporated herein by reference.

In some procedures, it may also be necessary to retrieve or aspirate theelectrically conductive fluid and/or the non-condensable gaseousproducts of ablation. In addition, it may be desirable to aspirate smallpieces of tissue or other body structures that are not completelydisintegrated by the high frequency energy, or other fluids at thetarget site, such as blood, mucus, the gaseous products of ablation,etc. Accordingly, the system of the present invention may include one ormore suction lumen(s) in the instrument, or on another instrument,coupled to a suitable vacuum source for aspirating fluids from thetarget site. In addition, the invention may include one or moreaspiration electrode(s) coupled to the distal end of the suction lumenfor ablating, or at least reducing the volume of, non-ablated tissuefragments that are aspirated into the lumen. The aspiration electrode(s)function mainly to inhibit clogging of the lumen that may otherwiseoccur as larger tissue fragments are drawn therein. The aspirationelectrode(s) may be different from the ablation active electrode(s), orthe same electrode(s) may serve both functions. A more completedescription of instruments incorporating aspiration electrode(s) can befound in commonly assigned, co-pending U.S. patent application Ser. No.09/010,382 filed Jan. 21, 1998, the complete disclosure of which isincorporated herein by reference.

As an alternative or in addition to suction, it may be desirable tocontain the excess electrically conductive fluid, tissue fragmentsand/or gaseous products of ablation at or near the target site with acontainment apparatus, such as a basket, retractable sheath, or thelike. This embodiment has the advantage of ensuring that the conductivefluid, tissue fragments or ablation products do not flow through thepatient's vasculature or into other portions of the body. In addition,it may be desirable to limit the amount of suction to limit theundesirable effect suction may have on hemostasis of severed bloodvessels.

The present invention may use a single active electrode or an array ofactive electrodes spaced around the distal surface of a catheter orprobe. In the latter embodiment, the electrode array usually includes aplurality of independently current-limited and/or power-controlledactive electrodes to apply electrical energy selectively to the targettissue while limiting the unwanted application of electrical energy tothe surrounding tissue and environment resulting from power dissipationinto surrounding electrically conductive fluids, such as blood, normalsaline, and the like. The active electrodes may be independentlycurrent-limited by isolating the terminals from each other andconnecting each terminal to a separate power source that is isolatedfrom the other active electrodes. Alternatively, the active electrodesmay be connected to each other at either the proximal or distal ends ofthe catheter to form a single wire that couples to a power source.

In one configuration, each individual active electrode in the electrodearray is electrically insulated from all other active electrodes in thearray within said instrument and is connected to a power source which isisolated from each of the other active electrodes in the array or tocircuitry which limits or interrupts current flow to the activeelectrode when low resistivity material (e.g., blood, electricallyconductive saline irrigant or electrically conductive gel) causes alower impedance path between the return electrode and the individualactive electrode. The isolated power sources for each individual activeelectrode may be separate power supply circuits having internalimpedance characteristics which limit power to the associated activeelectrode when a low impedance return path is encountered. By way ofexample, the isolated power source may be a user selectable constantcurrent source. In this embodiment, lower impedance paths willautomatically result in lower resistive heating levels since the heatingis proportional to the square of the operating current times theimpedance. Alternatively, a single power source may be connected to eachof the active electrodes through independently actuatable switches, orby independent current limiting elements, such as inductors, capacitors,resistors and/or combinations thereof. The current limiting elements maybe provided in the instrument, connectors, cable, controller, or alongthe conductive path from the controller to the distal tip of theinstrument. Alternatively, the resistance and/or capacitance may occuron the surface of the active electrode(s) due to oxide layers which formselected active electrodes (e.g., titanium or a resistive coating on thesurface of metal, such as platinum).

The tip region of the instrument may comprise many independent activeelectrodes designed to deliver electrical energy in the vicinity of thetip. The selective application of electrical energy to the conductivefluid is achieved by connecting each individual active electrode and thereturn electrode to a power source having independently controlled orcurrent limited channels. The return electrode(s) may comprise a singletubular member of conductive material proximal to the electrode array atthe tip which also serves as a conduit for the supply of theelectrically conductive fluid between the active and return electrodes.Alternatively, the instrument may comprise an array of return electrodesat the distal tip of the instrument (together with the activeelectrodes) to maintain the electric current at the tip. The applicationof high frequency voltage between the return electrode(s) and theelectrode array results in the generation of high electric fieldintensities at the distal tips of the active electrodes with conductionof high frequency current from each individual active electrode to thereturn electrode. The current flow from each individual active electrodeto the return electrode(s) is controlled by either active or passivemeans, or a combination thereof, to deliver electrical energy to thesurrounding conductive fluid while minimizing energy delivery tosurrounding (non-target) tissue.

The application of a high frequency voltage between the returnelectrode(s) and the active electrode(s) for appropriate time intervalseffects shrinking, cutting, removing, ablating, shaping, contracting orotherwise modifying the target tissue. In some embodiments of thepresent invention, the tissue volume over which energy is dissipated(i.e., a high current density exists) may be more precisely controlled,for example, by the use of a multiplicity of small active electrodeswhose effective diameters or principal dimensions range from about 10 mmto 0.01 mm, preferably from about 2 mm to 0.05 mm, and more preferablyfrom about 1 mm to 0.1 mm. In this embodiment, electrode areas for bothcircular and non-circular terminals will have a contact area (per mm²active electrode) below 50 mm ² for electrode arrays and as large as 75mm² for single electrode embodiments. In multiple electrode arrayembodiments, the contact area of each active electrode is typically inthe range from 0.0001 mm² to 1 mm², and more preferably from 0.001 mm²to 0.5 mm². The circumscribed area of the electrode array or activeelectrode is in the range from 0.25 mm² to 75 mm², preferably from 0.5mm² to 40 mm². In multiple electrode embodiments, the array will usuallyinclude at least two isolated active electrodes, often at least fiveactive electrodes, often greater than 10 active electrodes and even 50or more active electrodes, disposed over the distal contact surfaces onthe shaft. The use of small diameter active electrodes increases theelectric field intensity and reduces the extent or depth of tissueheating as a consequence of the divergence of current flux lines whichemanate from the exposed surface of each active electrode.

The area of the tissue treatment surface can vary widely, and the tissuetreatment surface can assume a variety of geometries, with particularareas and geometries being selected for specific applications. Thegeometries can be planar, concave, convex, hemispherical, conical,linear “in-line” array or virtually any other regular or irregularshape. Most commonly, the active electrode(s) or active electrode(s)will be formed at the distal tip of the electrosurgical instrumentshaft, frequently being planar, disk-shaped, or hemispherical surfacesfor use in reshaping procedures or being linear arrays for use incutting. Alternatively or additionally, the active electrode(s) may beformed on lateral surfaces of the electrosurgical instrument shaft(e.g., in the manner of a spatula), facilitating access to certain bodystructures in endoscopic procedures.

It should be clearly understood that the invention is not limited toelectrically isolated active electrodes, or even to a plurality ofactive electrodes. For example, the array of active electrodes may beconnected to a single lead that extends through the catheter shaft to apower source of high frequency current. Alternatively, the instrumentmay incorporate a single electrode that extends directly through thecatheter shaft or is connected to a single lead that extends to thepower source. The active electrode(s) may have ball shapes (e.g., fortissue vaporization and desiccation), twizzle shapes (for vaporizationand needle-like cutting), spring shapes (for rapid tissue debulking anddesiccation), twisted metal shapes, annular or solid tube shapes or thelike. Alternatively, the electrode(s) may comprise a plurality offilaments, rigid or flexible brush electrode(s) (for debulking a tumor,such as a fibroid, bladder tumor or a prostate adenoma), side-effectbrush electrode(s) on a lateral surface of the shaft, coiledelectrode(s) or the like.

In some embodiments, the electrode support and the fluid outlet may berecessed from an outer surface of the instrument or handpiece to confinethe electrically conductive fluid to the region immediately surroundingthe electrode support. In addition, the shaft may be shaped so as toform a cavity around the electrode support and the fluid outlet. Thishelps to assure that the electrically conductive fluid will remain incontact with the active electrode(s) and the return electrode(s) tomaintain the conductive path therebetween. In addition, this will helpto maintain a vapor layer and subsequent plasma layer between the activeelectrode(s) and the tissue at the treatment site throughout theprocedure, which reduces the thermal damage that might otherwise occurif the vapor layer were extinguished due to a lack of conductive fluid.Provision of the electrically conductive fluid around the target sitealso helps to maintain the tissue temperature at desired levels.

In other embodiments, the active electrodes are spaced from the tissue asufficient distance to minimize or avoid contact between the tissue andthe vapor layer formed around the active electrodes. In theseembodiments, contact between the heated electrons in the vapor layer andthe tissue is minimized as these electrons travel from the vapor layerback through the conductive fluid to the return electrode. The ionswithin the plasma, however, will have sufficient energy, under certainconditions such as higher voltage levels, to accelerate beyond the vaporlayer to the tissue. Thus, the tissue bonds are dissociated or broken asin previous embodiments, while minimizing the electron flow, and thusthe thermal energy, in contact with the tissue.

The electrically conductive fluid should have a threshold conductivityto provide a suitable conductive path between the return electrode andthe active electrode(s). The electrical conductivity of the fluid (inunits of millisiemens per centimeter or mS/cm) will usually be greaterthan 0.2 mS/cm, preferably will be greater than 2 mS/cm and morepreferably greater than 10 mS/cm. In an exemplary embodiment, theelectrically conductive fluid is isotonic saline, which has aconductivity of about 17 mS/cm. Applicant has found that a moreconductive fluid, or one with a higher ionic concentration, will usuallyprovide a more aggressive ablation rate. For example, a saline solutionwith higher levels of sodium chloride than conventional saline (which ison the order of about 0.9% sodium chloride) e.g., on the order ofgreater than 1% or between about 3% and 20%, may be desirable.Alternatively, the invention may be used with different types ofconductive fluids that increase the power of the plasma layer by, forexample, increasing the quantity of ions in the plasma, or by providingions that have higher energy levels than sodium ions. For example, thepresent invention may be used with elements other than sodium, such aspotassium, magnesium, calcium and other metals near the left end of theperiodic chart. In addition, other electronegative elements may be usedin place of chlorine, such as fluorine.

The voltage difference applied between the return electrode(s) and theactive electrode(s) will be at high or radio frequency, typicallybetween about 5 kHz and 20 MHz, usually being between about 30 kHz and2.5 MHz, preferably being between about 50 kHz and 500 kHz, often lessthan 350 kHz, and often between about 100 kHz and 200 kHz. In someapplications, applicant has found that a frequency of about 100 kHz isuseful because the tissue impedance is much greater at this frequency.In other applications, such as procedures in or around the heart or headand neck, higher frequencies may be desirable (e.g., 400–600 kHz) tominimize low frequency current flow into the heart or the nerves of thehead and neck. The RMS (root mean square) voltage applied will usuallybe in the range from about 5 volts to 1000 volts, preferably being inthe range from about 10 volts to 500 volts, often between about 150volts to 400 volts depending on the active electrode size, the operatingfrequency and the operation mode of the particular procedure or desiredeffect on the tissue (i.e., contraction, coagulation, cutting orablation). Typically, the peak-to-peak voltage for ablation or cuttingwith a square wave form will be in the range of 10 volts to 2000 voltsand preferably in the range of 100 volts to 1800 volts and morepreferably in the range of about 300 volts to 1500 volts, often in therange of about 300 volts to 800 volts peak to peak (again, depending onthe electrode size, number of electrons, the operating frequency and theoperation mode). Lower peak-to-peak voltages will be used for tissuecoagulation, thermal heating of tissue, or collagen contraction and willtypically be in the range from 50 to 1500, preferably 100 to 1000 andmore preferably 120 to 400 volts peak-to-peak (again, these values arecomputed using a square wave form). Higher peak-to-peak voltages, e.g.,greater than about 800 volts peak-to-peak, may be desirable for ablationof harder material, such as bone, depending on other factors, such asthe electrode geometries and the composition of the conductive fluid.

As discussed above, the voltage is usually delivered in a series ofvoltage pulses or alternating current of time varying voltage amplitudewith a sufficiently high frequency (e.g., on the order of 5 kHz to 20MHz) such that the voltage is effectively applied continuously (ascompared with e.g., lasers claiming small depths of necrosis, which aregenerally pulsed about 10 Hz to 20 Hz). In addition, the duty cycle(i.e., cumulative time in any one-second interval that energy isapplied) is on the order of about 50% for the present invention, ascompared with pulsed lasers which typically have a duty cycle of about0.0001%.

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being treated, and/or the maximum allowedtemperature selected for the instrument tip. The power source allows theuser to select the voltage level according to the specific requirementsof a particular neurosurgery procedure, cardiac surgery, arthroscopicsurgery, dermatological procedure, ophthalmic procedures, open surgeryor other endoscopic surgery procedure. For cardiac procedures andpotentially for neurosurgery, the power source may have an additionalfilter, for filtering leakage voltages at frequencies below 100 kHz,particularly voltages around 60 kHz. Alternatively, a power sourcehaving a higher operating frequency, e.g., 300 kHz to 600 kHz may beused in certain procedures in which stray low frequency currents may beproblematic. A description of one suitable power source can be found inco-pending patent application Ser. Nos. 09/058,571 and 09/058,336, filedApr. 10, 1998 the complete disclosure of both applications areincorporated herein by reference for all purposes.

The power source may be current limited or otherwise controlled so thatundesired heating of the target tissue or surrounding (non-target)tissue does not occur. In a presently preferred embodiment of thepresent invention, current limiting inductors are placed in series witheach independent active electrode, where the inductance of the inductoris in the range of 10 uH to 50,000 uH, depending on the electricalproperties of the target tissue, the desired tissue heating rate and theoperating frequency. Alternatively, capacitor-inductor (LC) circuitstructures may be employed, as described previously in U.S. Pat. No.5,697,909, the complete disclosure of which is incorporated herein byreference. Additionally, current limiting resistors may be selected.Preferably, these resistors will have a large positive temperaturecoefficient of resistance so that, as the current level begins to risefor any individual active electrode in contact with a low resistancemedium (e.g., saline irrigant or blood), the resistance of the currentlimiting resistor increases significantly, thereby minimizing the powerdelivery from said active electrode into the low resistance medium(e.g., saline irrigant or blood).

Referring to FIG. 1, an exemplary electrosurgical system 11 fortreatment of tissue in the spine will now be described in detail.Electrosurgical system 11 generally comprises an electrosurgicalhandpiece or probe 10 connected to a power supply 28 for providing highfrequency voltage to a target site, and a fluid source 21 for supplyingelectrically conductive fluid 50 to probe 10. In addition,electrosurgical system 11 may include an endoscope (not shown) with afiber optic head light for viewing the surgical site. The endoscope maybe integral with probe 10, or it may be part of a separate instrument.The system 11 may also include a vacuum source (not shown) for couplingto a suction lumen or tube 211 (see FIG. 4) in the probe 10 foraspirating the target site.

As shown, probe 10 generally includes a proximal handle 19 and anelongate shaft 18 having an array 12 of active electrodes 58 at itsdistal end. A connecting cable 34 has a connector 26 for electricallycoupling the active electrodes 58 to power supply 28. The activeelectrodes 58 are electrically isolated from each other and each ofelectrodes 58 is connected to an active or passive control networkwithin power supply 28 by means of a plurality of individually insulatedconductors (not shown). A fluid supply tube 15 is connected to a fluidtube 14 of probe 10 for supplying electrically conductive fluid 50 tothe target site. Fluid supply tube 15 may be connected to a suitablepump (not shown), if desired.

Power supply 28 has an operator controllable voltage level adjustment 30to change the applied voltage level, which is observable at a voltagelevel display 32. Power supply 28 also includes first, second and thirdfoot pedals 37, 38, 39 and a cable 36 which is removably coupled topower supply 28. The foot pedals 37, 38, 39 allow the surgeon toremotely adjust the energy level applied to active electrodes 58. In anexemplary embodiment, first foot pedal 37 is used to place the powersupply into the “ablation” mode and second foot pedal 38 places powersupply 28 into the “sub-ablation” mode (e.g., for coagulation orcontraction of tissue). The third foot pedal 39 allows the user toadjust the voltage level within the “ablation” mode. In the ablationmode, a sufficient voltage is applied to the active electrodes toestablish the requisite conditions for molecular dissociation of thetissue (i.e., vaporizing a portion of the electrically conductive fluid,ionizing charged particles within the vapor layer and accelerating thesecharged particles against the tissue). As discussed above, the requisitevoltage level for ablation will vary depending on the number, size,shape and spacing of the electrodes, the distance in which theelectrodes extend from the support member, etc. Once the surgeon placesthe power supply in the “ablation” mode, voltage level adjustment 30 orthird foot pedal 39 may be used to adjust the voltage level to adjustthe degree or aggressiveness of the ablation.

Of course, it will be recognized that the voltage and modality of thepower supply may be controlled by other input devices. However,applicant has found that foot pedals are convenient methods ofcontrolling the power supply while manipulating the probe during asurgical procedure.

In the subablation mode, the power supply 28 applies a low enoughvoltage to the active electrodes to avoid vaporization of theelectrically conductive fluid and subsequent molecular dissociation ofthe tissue. The surgeon may automatically toggle the power supplybetween the ablation and sub-ablation modes by alternately stepping onfoot pedals 37, 38, respectively. In some embodiments, this allows thesurgeon to quickly move between coagulation/thermal heating and ablationin situ, without having to remove his/her concentration from thesurgical field or without having to request an assistant to switch thepower supply. By way of example, as the surgeon is sculpting soft tissuein the ablation mode, the probe typically will simultaneously sealand/or coagulation small severed vessels within the tissue. However,larger vessels, or vessels with high fluid pressures (e.g., arterialvessels) may not be sealed in the ablation mode. Accordingly, thesurgeon can simply step on foot pedal 38, automatically lowering thevoltage level below the threshold level for ablation, and applysufficient pressure onto the severed vessel for a sufficient period oftime to seal and/or coagulate the vessel. After this is completed, thesurgeon may quickly move back into the ablation mode by stepping on footpedal 37.

Referring now to FIGS. 2 and 3, a representative high frequency powersupply for use according to the principles of the present invention willnow be described. The high frequency power supply of the presentinvention is configured to apply a high frequency voltage of about 10volts RMS to 500 volts RMS between one or more active electrodes (and/orcoagulation electrode) and one or more return electrodes. In theexemplary embodiment, the power supply applies about 70 volts RMS to 350volts RMS in the ablation mode and about 20 volts to 90 volts in asubablation mode, preferably 45 volts to 70 volts in the subablationmode (these values will, of course, vary depending on the probeconfiguration attached to the power supply and the desired mode ofoperation).

The preferred power source of the present invention delivers a highfrequency current selectable to generate average power levels rangingfrom several milliwatts to tens of watts per electrode, depending on thevolume of target tissue being treated, and/or the maximum allowedtemperature selected for the probe tip. The power supply allows the userto select the voltage level according to the specific requirements of aparticular procedure, e.g., spinal surgery, arthroscopic surgery,dermatological procedure, ophthalmic procedures, open surgery, or otherendoscopic surgery procedure.

As shown in FIG. 2, the power supply generally comprises a radiofrequency (RF) power oscillator 70 having output connections forcoupling via a power output signal 71 to the load impedance, which isrepresented by the electrode assembly when the electrosurgical probe isin use. In the representative embodiment, the RF oscillator operates atabout 100 kHz. The RF oscillator is not limited to this frequency andmay operate at frequencies of about 300 kHz to 600 kHz. In particular,for cardiac applications, the RF oscillator will preferably operate inthe range of about 400 kHz to about 600 kHz. The RF oscillator willgenerally supply a square wave signal with a crest factor of about 1 to2. Of course, this signal may be a sine wave signal or other suitablewave signal depending on the application and other factors, such as thevoltage applied, the number and geometry of the electrodes, etc. Thepower output signal 71 is designed to incur minimal voltage decrease(i.e., sag) under load. This improves the applied voltage to the activeelectrodes and the return electrode, which improves the rate ofvolumetric removal (ablation) of tissue.

Power is supplied to RF oscillator 70 by a switching power supply 72coupled between the power line and the RF oscillator rather than aconventional transformer. The switching power supply 72 allows powersupply 28 to achieve high peak power output without the large size andweight of a bulky transformer. The architecture of the switching powersupply also has been designed to reduce electromagnetic noise such thatU.S. and foreign EMI requirements are met. This architecture comprises azero voltage switching or crossing, which causes the transistors to turnON and OFF when the voltage is zero. Therefore, the electromagneticnoise produced by the transistors switching is vastly reduced. In anexemplary embodiment, the switching power supply 72 operates at about100 kHz.

A controller 74 coupled to the operator controls 73 (i.e., foot pedalsand voltage selector) and display 76, is connected to a control input ofthe switching power supply 72 for adjusting the generator output powerby supply voltage variation. The controller 74 may be a microprocessoror an integrated circuit. The power supply may also include one or morecurrent sensors 75 for detecting the output current. The power supply ispreferably housed within a metal casing which provides a durableenclosure for the electrical components therein. In addition, the metalcasing reduces the electromagnetic noise generated within the powersupply because the grounded metal casing functions as a “Faradayshield,” thereby shielding the environment from internal sources ofelectromagnetic noise.

The power supply generally comprises a main or mother board containinggeneric electrical components required for many different surgicalprocedures (e.g., arthroscopy, urology, general surgery, dermatology,neurosurgery, etc.), and a daughter board containing applicationspecific current-limiting circuitry (e.g., inductors, resistors,capacitors and the like). The daughter board is coupled to the motherboard by a detachable multi-pin connector to allow convenient conversionof the power supply to, e.g., applications requiring a different currentlimiting circuit design. For arthroscopy, for example, the daughterboard preferably comprises a plurality of inductors of about 200 to 400microhenries, usually about 300 microhenries, for each of the channelssupplying current to the active electrodes 102 (see FIG. 4).

Alternatively, in one embodiment, current limiting inductors are placedin series with each independent active electrode, where the inductanceof the inductor is in the range of 10 uH to 50,000 uH, depending on theelectrical properties of the target tissue, the desired tissue heatingrate and the operating frequency. Alternatively, capacitor-inductor (LC)circuit structures may be employed, as described previously inco-pending PCT application No. PCT/US94/05168, the complete disclosureof which is incorporated herein by reference. Additionally, currentlimiting resistors may be selected. Preferably, these resistors willhave a large positive temperature coefficient of resistance so that, asthe current level begins to rise for any individual active electrode incontact with a low resistance medium (e.g., saline irrigant orconductive gel), the resistance of the current limiting resistorincreases significantly, thereby minimizing the power delivery from saidactive electrode into the low resistance medium (e.g., saline irrigantor conductive gel). Power output signal may also be coupled to aplurality of current limiting elements 96, which are preferably locatedon the daughter board since the current limiting elements may varydepending on the application. A more complete description of arepresentative power supply can be found in commonly assigned U.S.patent application Ser. No. 09/058,571, previously incorporated hereinby reference.

FIGS. 4–6 illustrate an exemplary electrosurgical probe 20 constructedaccording to the principles of the present invention. As shown in FIG.4, probe 20 generally includes an elongated shaft 100 which may beflexible or rigid, a handle 204 coupled to the proximal end of shaft 100and an electrode support member 102 coupled to the distal end of shaft100. Shaft 100 preferably comprises an electrically conducting material,usually metal, which is selected from the group comprising tungsten,stainless steel alloys, platinum or its alloys, titanium or its alloys,molybdenum or its alloys, and nickel or its alloys. In this embodiment,shaft 100 includes an electrically insulating jacket 108, which istypically formed as one or more electrically insulating sheaths orcoatings, such as polytetrafluoroethylene, polyimide, and the like. Theprovision of the electrically insulating jacket over the shaft preventsdirect electrical contact between these metal elements and any adjacentbody structure or the surgeon. Such direct electrical contact between abody structure (e.g., tendon) and an exposed electrode could result inunwanted heating and necrosis of the structure at the point of contactcausing necrosis. Alternatively, the return electrode may comprise anannular band coupled to an insulating shaft and having a connectorextending within the shaft to its proximal end.

Handle 204 typically comprises a plastic material that is easily moldedinto a suitable shape for handling by the surgeon. Handle 204 defines aninner cavity (not shown) that houses the electrical connections 250(FIG. 6), and provides a suitable interface for connection to anelectrical connecting cable distal portion 22 (see FIG. 1) Electrodesupport member 102 extends from the distal end of shaft 100 (usuallyabout 1 mm to 20 mm), and provides support for a plurality ofelectrically isolated active electrodes 104 (see FIG. 5). As shown inFIG. 4, a fluid tube 233 extends through an opening in handle 204, andincludes a connector 235 for connection to a fluid supply source, forsupplying electrically conductive fluid to the target site. Depending onthe configuration of the distal surface of shaft 100, fluid tube 233 mayextend through a single lumen (not shown) in shaft 100, or it may becoupled to a plurality of lumens (also not shown) that extend throughshaft 100 to a plurality of openings at its distal end. In therepresentative embodiment, tubing 239 is a tube that extends along theexterior of shaft 100 to a point just distal of return electrode 112(see FIG. 5). In this embodiment, the fluid is directed through anopening 237 past return electrode 112 to the active electrodes 104.Probe 20 may also include a valve 17 (FIG. 1) or equivalent structurefor controlling the flow rate of the electrically conductive fluid tothe target site.

As shown in FIG. 4, the distal portion of shaft 100 is preferably bentto improve access to the operative site of the tissue being treated.Electrode support member 102 has a substantially planar tissue treatmentsurface 212 (FIG. 5) that is usually at an angle of about 10 degrees to90 degrees relative to the longitudinal axis of shaft 100, preferablyabout 30 degrees to 60 degrees and more preferably about 45 degrees. Inalternative embodiments, the distal portion of shaft 100 comprises aflexible material which can be deflected relative to the longitudinalaxis of the shaft. Such deflection may be selectively induced bymechanical tension of a pull wire, for example, or by a shape memorywire that expands or contracts by externally applied temperaturechanges. A more complete description of this embodiment can be found inU.S. Pat. No. 5,697,909, the complete disclosure of which has previouslybeen incorporated herein by reference. Alternatively, the shaft 100 ofthe present invention may be bent by the physician to the appropriateangle using a conventional bending tool or the like.

In the embodiment shown in FIGS. 4 to 6, probe 20 includes a returnelectrode 112 for completing the current path between active electrodes104 and a high frequency power supply 28 (see FIG. 1). As shown, returnelectrode 112 preferably comprises an exposed portion of shaft 100shaped as an annular conductive band near the distal end of shaft 100slightly proximal to tissue treatment surface 212 of electrode supportmember 102, typically about 0.5 mm to 10 mm and more preferably about 1mm to 10 mm. Return electrode 112 or shaft 100 is coupled to a connector258 that extends to the proximal end of probe 10/20, where it issuitably connected to power supply 28 (FIG. 1).

As shown in FIG. 4, return electrode 112 is not directly connected toactive electrodes 104. To complete this current path so that activeelectrodes 104 are electrically connected to return electrode 112, anelectrically conductive fluid (e.g., isotonic saline) is caused to flowtherebetween. In the representative embodiment, the electricallyconductive fluid is delivered through fluid tube 233 to opening 237, asdescribed above. Alternatively, the conductive fluid may be delivered bya fluid delivery element (not shown) that is separate from probe 20. Inarthroscopic surgery, for example, the target area of the joint will beflooded with isotonic saline and the probe 90 will be introduced intothis flooded target area. Electrically conductive fluid can becontinually resupplied to maintain the conduction path between returnelectrode 112 and active electrodes 104. In other embodiments, thedistal portion of probe 20 may be dipped into a source of electricallyconductive fluid, such as a gel or isotonic saline, prior to positioningat the target site. Applicant has found that the surface tension of thefluid and/or the viscous nature of a gel allows the conductive fluid toremain around the active and return electrodes for long enough tocomplete its function according to the present invention, as describedbelow. Alternatively, the conductive fluid, such as a gel, may beapplied directly to the target site.

In alternative embodiments, the fluid path may be formed in probe 90 by,for example, an inner lumen or an annular gap between the returnelectrode and a tubular support member within shaft 100 (see FIGS. 8Aand 8B). This annular gap may be formed near the perimeter of the shaft100 such that the electrically conductive fluid tends to flow radiallyinward towards the target site, or it may be formed towards the centerof shaft 100 so that the fluid flows radially outward. In both of theseembodiments, a fluid source (e.g., a bag of fluid elevated above thesurgical site or having a pumping device), is coupled to probe 90 via afluid supply tube (not shown) that may or may not have a controllablevalve. A more complete description of an electrosurgical probeincorporating one or more fluid lumen(s) can be found in U.S. Pat. No.5,697,281, the complete disclosure of which has previously beenincorporated herein by reference.

Referring to FIG. 5, the electrically isolated active electrodes 104 arespaced apart over tissue treatment surface 212 of electrode supportmember 102. The tissue treatment surface and individual activeelectrodes 104 will usually have dimensions within the ranges set forthabove. In the representative embodiment, the tissue treatment surface212 has a circular cross-sectional shape with a diameter in the range of1 mm to 20 mm. The individual active electrodes 104 preferably extendoutward from tissue treatment surface 212 by a distance of about 0.1 mmto 4 mm, usually about 0.2 mm to 2 mm. Applicant has found that thisconfiguration increases the high electric field intensities andassociated current densities around active electrodes 104 to facilitatethe ablation and shrinkage of tissue as described in detail above.

In the embodiment of FIGS. 4 to 6, the probe includes a single, largeropening 209 in the center of tissue treatment surface 212, and aplurality of active electrodes (e.g., about 3–15) around the perimeterof surface 212 (see FIG. 5). Alternatively, the probe may include asingle, annular, or partially annular, active electrode at the perimeterof the tissue treatment surface. The central opening 209 is coupled to asuction lumen (not shown) within shaft 100 and a suction tube 211 (FIG.4) for aspirating tissue, fluids and/or gases from the target site. Inthis embodiment, the electrically conductive fluid generally flowsradially inward past active electrodes 104 and then back through theopening 209. Aspirating the electrically conductive fluid during surgeryallows the surgeon to see the target site, and it prevents the fluidfrom flowing into the patient's body.

Of course, it will be recognized that the distal tip of anelectrosurgical probe of the invention, e.g. probe Oct. 20, 1990, mayhave a variety of different configurations. For example, the probe mayinclude a plurality of openings 209 around the outer perimeter of tissuetreatment surface 212 (see FIG. 7B). In this embodiment, the activeelectrodes 104 extend distally from the center of tissue treatmentsurface 212 such that they are located radially inward from openings209. The openings are suitably coupled to fluid tube 233 for deliveringelectrically conductive fluid to the target site, and suction tube 211for aspirating the fluid after it has completed the conductive pathbetween the return electrode 112 and the active electrodes 104.

FIG. 6 illustrates the electrical connections 250 within handle 204 forcoupling active electrodes 104 and return electrode 112 to the powersupply 28. As shown, a plurality of wires 252 extend through shaft 100to couple active electrodes 104 to a plurality of pins 254, which areplugged into a connector block 256 for coupling to a connecting cabledistal end 22 (FIG. 1). Similarly, return electrode 112 is coupled toconnector block 256 via a wire 258 and a plug 260.

According to the present invention, the probe 20 further includes anidentification element that is characteristic of the particularelectrode assembly so that the same power supply 28 can be used fordifferent electrosurgical operations. In one embodiment, for example,the probe (e.g., 20) includes a voltage reduction element or a voltagereduction circuit for reducing the voltage applied between the activeelectrodes 104 and the return electrode 112. The voltage reductionelement serves to reduce the voltage applied by the power supply so thatthe voltage between the active electrodes and the return electrode islow enough to avoid excessive power dissipation into the electricallyconducting medium and/or ablation of the soft tissue at the target site.In some embodiments, the voltage reduction element allows the powersupply 28 to apply two different voltages simultaneously to twodifferent electrodes (see FIG. 1 SD). In other embodiments, the voltagereduction element primarily allows the electrosurgical probe to becompatible with various electrosurgical generators supplied byArthroCare Corporation (Sunnyvale, Calif.) that are adapted to applyhigher voltages for ablation or vaporization of tissue. For thermalheating or coagulation of tissue, for example, the voltage reductionelement will serve to reduce a voltage of about 100 volts rms to 170volts rms (which is a setting of 1 or 2 on the ArthroCare Model 970 and980 (i.e., 2000) Generators) to about 45 volts rms to 60 volts rms,which is a suitable voltage for coagulation of tissue without ablation(e.g., molecular dissociation) of the tissue.

Of course, for some procedures, the probe will typically not require avoltage reduction element. Alternatively, the probe may include avoltage increasing element or circuit, if desired. Alternatively oradditionally, the cable 34 and/or cable distal end 22 that couples thepower supply 28 to the probe may be used as a voltage reduction element.The cable has an inherent capacitance that can be used to reduce thepower supply voltage if the cable is placed into the electrical circuitbetween the power supply, the active electrodes and the returnelectrode. In this embodiment, the cable distal end 22 may be usedalone, or in combination with one of the voltage reduction elementsdiscussed above, e.g., a capacitor. Further, it should be noted that thepresent invention can be used with a power supply that is adapted toapply a voltage within the selected range for treatment of tissue. Inthis embodiment, a voltage reduction element or circuitry may not bedesired.

FIGS. 8A–8C schematically illustrate the distal portion of threedifferent embodiments of probe 90 according to the present invention. Asshown in FIG. 8A, active electrodes 104 are anchored in a support matrix102′ of suitable insulating material (e.g., silicone or a ceramic orglass material, such as alumina, zirconia and the like) which could beformed at the time of manufacture in a flat, hemispherical or othershape according to the requirements of a particular procedure. Thepreferred support matrix material is alumina, available from KyoceraIndustrial Ceramics Corporation, Elkgrove, Ill., because of its highthermal conductivity, good electrically insulative properties, highflexural modulus, resistance to carbon tracking, biocompatibility, andhigh melting point. The support matrix 102′ is adhesively joined to atubular support member 78 that extends most or all of the distancebetween matrix 102′ and the proximal end of probe 90. Tubular member 78preferably comprises an electrically insulating material, such as anepoxy or silicone-based material.

In a preferred construction technique, active electrodes 104 extendthrough pre-formed openings in the support matrix 102′ so that theyprotrude above tissue treatment surface 212 by the desired distance. Theelectrodes are then bonded to the tissue treatment surface 212 ofsupport matrix 102′, typically by an inorganic sealing material 80.Sealing material 80 is selected to provide effective electricalinsulation, and good adhesion to both support matrix 102′ and theplatinum or titanium active electrodes. Sealing material 80 additionallyshould have a compatible thermal expansion coefficient and a meltingpoint well below that of platinum or titanium and alumina or zirconia,typically being a glass or glass ceramic.

In the embodiment shown in FIG. 8A, return electrode 112 comprises anannular member positioned around the exterior of shaft 100 of probe 90.Return electrode 112 may fully or partially circumscribe tubular supportmember 78 to form an annular gap 54 therebetween for flow ofelectrically conductive liquid 50 therethrough, as discussed below. Gap54 preferably has a width in the range of 0.25 mm to 4 mm.Alternatively, probe 90 may include a plurality of longitudinal ribsbetween support member 78 and return electrode 112 to form a pluralityof fluid lumens extending along the perimeter of shaft 100. In thisembodiment, the plurality of lumens will extend to a plurality ofopenings.

Return electrode 112 is disposed within an electrically insulativejacket 118, which is typically formed as one or more electricallyinsulative sheaths or coatings, such as polytetrafluoroethylene,polyimide, and the like. The provision of the electrically insulativejacket 118 over return electrode 112 prevents direct electrical contactbetween return electrode 112 and any adjacent body structure. Suchdirect electrical contact between a body structure (e.g., tendon) and anexposed return electrode 112 could result in unwanted heating andnecrosis of the structure at the point of contact.

As shown in FIG. 8A, return electrode 112 is not directly connected toactive electrodes 104. To complete this current path so that terminals104 are electrically connected to return electrode 112, electricallyconducting liquid 50 (e.g., isotonic saline) is caused to flow alongfluid path(s) 83. Fluid path 83 is formed by annular gap 54 betweenreturn electrode 112 and tubular support member 78. The electricallyconducting liquid 50 flowing through fluid path 83 provides a pathwayfor electrical current flow between active electrodes 104 and returnelectrode 112, as illustrated by the current flux lines 60 in FIG. 8A.When a voltage difference is applied between active electrodes 104 andreturn electrode 112, high electric field intensities will be generatedat the distal tips of active electrodes 104 with current flow fromactive electrodes 104 through the target tissue to return electrode 112,the high electric field intensities causing ablation of tissue 52 inzone 88.

FIG. 8B illustrates another alternative embodiment of electrosurgicalprobe 90 which has a return electrode 112 positioned within tubularmember 78. Return electrode 112 is preferably a tubular member definingan inner lumen 57 for allowing electrically conducting liquid 50 (e.g.,isotonic saline) to flow therethrough in electrical contact with returnelectrode 112. In this embodiment, a voltage difference is appliedbetween active electrodes 104 and return electrode 112 resulting inelectrical current flow through the electrically conducting liquid 50 asshown by current flux lines 60. As a result of the applied voltagedifference and concomitant high electric field intensities at the tipsof active electrodes 104, tissue 52 becomes ablated or transected inzone 88.

FIG. 8C illustrates another embodiment of probe 90 that is a combinationof the embodiments in FIGS. 8A and 8B. As shown, this probe includesboth an inner lumen 57 and an outer gap or plurality of outer lumens 54for flow of electrically conductive fluid. In this embodiment, thereturn electrode 112 may be positioned within tubular member 78 as inFIG. 8B, outside of tubular member 78 as in FIG. 8A, or in bothlocations.

In some embodiments, the probe 20/90 will also include one or moreaspiration electrode(s) coupled to the aspiration lumen for inhibitingclogging during aspiration of tissue fragments from the surgical site.As shown in FIG. 9, one or more of the active electrodes 104 maycomprise loop electrodes 140 that extend across distal opening 209 ofthe suction lumen within shaft 100. In the representative embodiment,two of the active electrodes 104 comprise loop electrodes 140 that crossover the distal opening 209. Of course, it will be recognized that avariety of different configurations are possible, such as a single loopelectrode, or multiple loop electrodes having different configurationsthan shown. In addition, the electrodes may have shapes other thanloops, such as the coiled configurations shown in FIGS. 10 and 11.Alternatively, the electrodes may be formed within suction lumenproximal to the distal opening 209, as shown in FIG. 13. The mainfunction of loop electrodes 140 is to ablate portions of tissue that aredrawn into the suction lumen to prevent clogging of the lumen.

In some embodiments, loop electrodes 140 are electrically isolated fromthe other active electrodes 104. In other embodiments, the loopelectrodes 140 and active electrodes 104 may be electrically connectedto each other such that both are activated together. Loop electrodes 140may or may not be electrically isolated from each other. Loop electrodes140 will usually extend only about 0.05 mm to 4 mm, preferably about 0.1mm to 1 mm from the tissue treatment surface of electrode support member102.

Referring now to FIGS. 10 and 11, alternative embodiments for aspirationelectrodes will now be described. As shown in FIG. 10, the aspirationelectrodes may comprise a pair of coiled electrodes 150 that extendacross distal opening 209 of the suction lumen. The larger surface areaof the coiled electrodes 150 usually increases the effectiveness of theelectrodes 150 in ablating tissue fragments which may approach or passthrough opening 209. In FIG. 11, the aspiration electrode comprises asingle coiled electrode 154 extending across the distal opening 209 ofthe suction lumen. This single electrode 152 may be sufficient toinhibit clogging of the suction lumen. Alternatively, the aspirationelectrodes may be positioned within the suction lumen proximal to thedistal opening 209. Preferably, these electrodes are close to opening209 so that tissue does not clog the opening 209 before it reacheselectrodes 154. In this embodiment, a separate return electrode (notshown) may be provided within the suction lumen to confine the electriccurrents therein.

Referring to FIG. 12, another embodiment of the present inventionincorporates a wire mesh electrode 600 extending across the distalportion of aspiration lumen 162. As shown, mesh electrode 600 includes aplurality of openings 602 to allow fluids and tissue fragments to flowtherethrough into aspiration lumen 162. The size of the openings 602will vary depending on a variety of factors. The mesh electrode may becoupled to the distal or proximal surfaces of support member 102. Wiremesh electrode 600 comprises a conductive material, such as titanium,tantalum, steel, stainless steel, tungsten, copper, gold or the like. Inthe representative embodiment, wire mesh electrode 600 comprises adifferent material having a different electric potential than the activeelectrode(s) 104. Preferably, mesh electrode 600 comprises steel andactive electrode(s) 104 comprises tungsten. Applicant has found that aslight variance in the electrochemical potential of mesh electrode 600and active electrode(s) 104 improves the performance of the device. Ofcourse, it will be recognized that mesh electrode 600 may beelectrically insulated from active electrode(s) 104, as in previousembodiments.

Referring to FIG. 13, another embodiment of the present inventionincorporates an aspiration electrode 160 within an aspiration lumen 162of the probe. As shown, the electrode 160 is positioned just proximal ofdistal opening 209 so that the tissue fragments are ablated as theyenter lumen 162. In the representative embodiment, aspiration electrode160 comprises a loop electrode that extends across the aspiration lumen162. However, it will be recognized that many other configurations arepossible. In this embodiment, the return electrode 164 is locatedtowards the exterior of the shaft, as in the previously describedembodiments. Alternatively, the return electrode(s) may be locatedwithin the aspiration lumen 162 with the aspiration electrode 160. Forexample, the inner insulating coating 163 may be exposed at portionswithin the lumen 162 to provide a conductive path between this exposedportion of return electrode 164 and the aspiration electrode 160. Thelatter embodiment has the advantage of confining the electric currentsto within the aspiration lumen. In addition, in dry fields in which theconductive fluid is delivered to the target site, it is usually easierto maintain a conductive fluid path between the active and returnelectrodes in the latter embodiment because the conductive fluid isaspirated through the aspiration lumen 162 along with the tissuefragments.

Referring now to FIGS. 14A–14C, an alternative embodiment incorporatinga metal screen 610 is illustrated. As shown, metal screen 610 has aplurality of peripheral openings 612 for receiving active electrodes104, and a plurality of inner openings 614 for allowing aspiration offluid and tissue through an opening 609 of the aspiration lumen. Asshown, screen 610 is press fitted over active electrodes 104 and thenadhered to shaft 100 of probe 20/90. Similar to the mesh electrodeembodiment, metal screen 610 may comprise a variety of conductivemetals, such as titanium, tantalum, steel, stainless steel, tungsten,copper, gold or the like. In the representative embodiment, metal screen610 is coupled directly to, or integral with, active electrode(s) 104.In this embodiment, the active electrode(s) 104 and the metal screen 610are electrically coupled to each other.

FIGS. 15A to 15D illustrate embodiments of an electrosurgical probe 350specifically designed for the treatment of herniated or diseased spinaldiscs. Referring to FIG. 15A, probe 350 comprises an electricallyconductive shaft 352, a handle 354 coupled to the proximal end of shaft352 and an electrically insulating support member 356 at the distal endof shaft 352. Probe 350 further includes a shrink wrapped insulatingsleeve 358 over shaft 352, and an exposed portion of shaft 352 thatfunctions as the return electrode 360. In the representative embodiment,probe 350 comprises a plurality of active electrodes 362 extending fromthe distal end of support member 356. As shown, return electrode 360 isspaced a further distance from active electrodes 362 than in theembodiments described above. In this embodiment, the return electrode360 is spaced a distance of about 2.0 mm to 50 mm, preferably about 5 mmto 25 mm from active electrodes 362. In addition, return electrode 360has a larger exposed surface area than in previous embodiments, having alength in the range of about 2.0 mm to 40 mm, preferably about 5 mm to20 mm. Accordingly, electric current passing from active electrodes 362to return electrode 360 will follow a current flow path 370 that isfurther away from shaft 352 than in the previous embodiments. In someapplications, this current flow path 370 results in a deeper currentpenetration into the surrounding tissue with the same voltage level, andthus increased thermal heating of the tissue. As discussed above, thisincreased thermal heating may have advantages in some applications oftreating disc or other spinal abnormalities. Typically, it is desired toachieve a tissue temperature in the range of about 60° C. to 100° C. toa depth of about 0.2 mm to 5 mm, usually about 1 mm to 2 mm. The voltagerequired for this thermal damage will partly depend on the electrodeconfigurations, the conductivity of the tissue and the area immediatelysurrounding the electrodes, the time period in which the voltage isapplied and the depth of tissue damage desired. With the electrodeconfigurations described in FIGS. 15A–15D, the voltage level for thermalheating will usually be in the range of about 20 volts rms to 300 voltsrms, preferably about 60 volts rms to 200 volts rms. The peak-to-peakvoltages for thermal heating with a square wave form having a crestfactor of about 2 are typically in the range of about 40 to 600 voltspeak-to-peak, preferably about 120 to 400 volts peak-to-peak. The higherthe voltage is within this range, the less time required. If the voltageis too high, however, the surface tissue may be vaporized, debulked orablated, which is undesirable.

In alternative embodiments, the electrosurgical system used inconjunction with probe 350 may include a dispersive return electrode 450(see FIG. 16) for switching between bipolar and monopolar modes. In thisembodiment, the system will switch between an ablation mode, where thedispersive pad 450 is deactivated and voltage is applied between activeand return electrodes 362, 360, and a subablation or thermal heatingmode, where the active electrode(s) 362 are deactivated and voltage isapplied between the dispersive pad 450 and the return electrode 360. Inthe subablation mode, a lower voltage is typically applied and thereturn electrode 360 functions as the active electrode to providethermal heating and/or coagulation of tissue surrounding returnelectrode 360.

FIG. 15B illustrates yet another embodiment of the present invention. Asshown, electrosurgical probe 350 comprises an electrode assembly 372having one or more active electrode(s) 362 and a proximally spacedreturn electrode 360 as in previous embodiments. Return electrode 360 istypically spaced about 0.5 mm to 25 mm, preferably 1.0 mm to 5.0 mm fromthe active electrode(s) 362, and has an exposed length of about 1 mm to20 mm. In addition, electrode assembly 372 includes two additionalelectrodes 374, 376 spaced axially on either side of return electrode360. Electrodes 374, 376 are typically spaced about 0.5 mm to 25 mm,preferably about 1 mm to 5 mm from return electrode 360. In therepresentative embodiment, the additional electrodes 374, 376 areexposed portions of shaft 352, and the return electrode 360 iselectrically insulated from shaft 352 such that a voltage difference maybe applied between electrodes 374, 376 and electrode 360. In thisembodiment, probe 350 may be used in at least two different modes, anablation mode and a subablation or thermal heating mode. In the ablationmode, voltage is applied between active electrode(s) 362 and returnelectrode 360 in the presence of electrically conductive fluid, asdescribed above. In the ablation mode, electrodes 374, 376 aredeactivated. In the thermal heating or coagulation mode, activeelectrode(s) 362 are deactivated and a voltage difference is appliedbetween electrodes 374, 376 and electrode 360 such that a high frequencycurrent 370 flows therebetween, as shown in FIG. 15B. In the thermalheating mode, a lower voltage is typically applied below the thresholdfor plasma formation and ablation, but sufficient to cause some thermaldamage to the tissue immediately surrounding the electrodes withoutvaporizing or otherwise debulking this tissue so that the current 370provides thermal heating and/or coagulation of tissue surroundingelectrodes 360, 372, 374.

FIG. 15C illustrates another embodiment of probe 350 incorporating anelectrode assembly 372 having one or more active electrode(s) 362 and aproximally spaced return electrode 360 as in previous embodiments.Return electrode 360 is typically spaced about 0.5 mm to 25 mm,preferably 1.0 mm to 5.0 mm from the active electrode(s) 362, and has anexposed length of about 1 mm to 20 mm. In addition, electrode assembly372 includes a second active electrode 380 separated from returnelectrode 360 by an electrically insulating spacer 382. In thisembodiment, handle 354 includes a switch 384 for toggling probe 350between at least two different modes, an ablation mode and a subablationor thermal heating mode. In the ablation mode, voltage is appliedbetween active electrode(s) 362 and return electrode 360 in the presenceof electrically conductive fluid, as described above. In the ablationmode, electrode 380 is deactivated. In the thermal heating orcoagulation mode, active electrode(s) 362 may be deactivated and avoltage difference is applied between electrode 380 and electrode 360such that a high frequency current 370 flows therebetween.Alternatively, active electrode(s) 362 may not be deactivated as thehigher resistance of the smaller electrodes may automatically send theelectric current to electrode 380 without having to physically decoupleelectrode(s) 362 from the circuit. In the thermal heating mode, a lowervoltage is typically applied below the threshold for plasma formationand ablation, but sufficient to cause some thermal damage to the tissueimmediately surrounding the electrodes without vaporizing or otherwisedebulking this tissue so that the current 370 provides thermal heatingand/or coagulation of tissue surrounding electrodes 360, 380.

Of course, it will be recognized that a variety of other embodiments maybe used to accomplish similar functions as the embodiments describedabove. For example, electrosurgical probe 350 may include a plurality ofhelical bands formed around shaft 352, with one or more of the helicalbands having an electrode coupled to the portion of the band such thatone or more electrodes are formed on shaft 352 spaced axially from eachother.

FIG. 15D illustrates another embodiment of the invention designed forchanneling through tissue and creating lesions therein to treat spinaldiscs and/or snoring and sleep apnea. As shown, probe 350 is similar tothe probe in FIG. 15C having a return electrode 360 and a third,coagulation electrode 380 spaced proximally from the return electrode360. In this embodiment, active electrode 362 comprises a singleelectrode wire extending distally from insulating support member 356. Ofcourse, the active electrode 362 may have a variety of configurations toincrease the current densities on its surfaces, e.g., a conical shapetapering to a distal point, a hollow cylinder, loop electrode and thelike. In the representative embodiment, support members 356 and 382 areconstructed of a material, such as ceramic, glass, silicone and thelike. The proximal support member 382 may also comprise a moreconventional organic material as this support member 382 will generallynot be in the presence of a plasma that would otherwise etch or wearaway an organic material.

The probe 350 in FIG. 15D does not include a switching element. In thisembodiment, all three electrodes are activated when the power supply isactivated. The return electrode 360 has an opposite polarity from theactive and coagulation electrodes 362, 380 such that current 370 flowsfrom the latter electrodes to the return electrode 360 as shown. In thepreferred embodiment, the electrosurgical system includes a voltagereduction element or a voltage reduction circuit for reducing thevoltage applied between the coagulation electrode 380 and returnelectrode 360. The voltage reduction element allows the power supply 28to, in effect, apply two different voltages simultaneously to twodifferent electrodes. Thus, for channeling through tissue, the operatormay apply a voltage sufficient to provide ablation of the tissue at thetip of the probe (i.e., tissue adjacent to the active electrode 362). Atthe same time, the voltage applied to the coagulation electrode 380 willbe insufficient to ablate tissue. For thermal heating or coagulation oftissue, for example, the voltage reduction element will serve to reducea voltage of about 100 volts rms to 300 volts rms to about 45 volts rmsto 90 volts rms, which is a suitable voltage for coagulation of tissuewithout ablation (e.g., molecular dissociation) of the tissue.

In the representative embodiment, the voltage reduction elementcomprises a pair of capacitors forming a bridge divider (not shown)coupled to the power supply and coagulation electrode 380. Thecapacitors usually have a capacitance of about 200 pF to 500 pF (at 500volts) and preferably about 300 pF to 350 pF (at 500 volts). Of course,the capacitors may be located in other places within the system, such asin, or distributed along the length of, the cable, the generator, theconnector, etc. In addition, it will be recognized that other voltagereduction elements, such as diodes, transistors, inductors, resistors,capacitors or combinations thereof, may be used in conjunction with thepresent invention. For example, the probe 350 may include a codedresistor (not shown) that is constructed to lower the voltage appliedbetween the return and coagulation electrodes 360, 380, respectively. Inaddition, electrical circuits may be employed for this purpose.

Of course, for some procedures, the probe will typically not require avoltage reduction element. Alternatively, the probe may include avoltage increasing element or circuit, if desired. Alternatively oradditionally, cable 22/34 that couples power supply 28 to the probe 90may be used as a voltage reduction element. The cable has an inherentcapacitance that can be used to reduce the power supply voltage if thecable is placed into the electrical circuit between the power supply,the active electrodes and the return electrode. In this embodiment,cable 22/34 may be used alone, or in combination with one of the voltagereduction elements discussed above, e.g., a capacitor. Further, itshould be noted that the present invention can be used with a powersupply that is adapted to apply two different voltages within theselected range for treatment of tissue. In this embodiment, a voltagereduction element or circuitry may not be desired.

In one specific embodiment, the probe 350 is manufactured by firstinserting an electrode wire (active electrode 362) through a ceramictube (insulating member 356) such that a distal portion of the wireextends through the distal portion of the tube, and bonding the wire tothe tube, typically with an appropriate epoxy. A stainless steel tube(return electrode 360) is then placed over the proximal portion of theceramic tube, and a wire (e.g., nickel wire) is bonded, typically byspot welding, to the inside surface of the stainless steel tube. Thestainless steel tube is coupled to the ceramic tube by epoxy, and thedevice is cured in an oven or other suitable heat source. A secondceramic tube (insulating member 382) is then placed inside of theproximal portion of the stainless steel tube, and bonded in a similarmanner. The shaft 358 is then bonded to the proximal portion of thesecond ceramic tube, and an insulating sleeve (e.g. polyimide) iswrapped around shaft 358 such that only a distal portion of the shaft isexposed (i.e., coagulation electrode 380). The nickel wire connectionwill extend through the center of shaft 358 to connect return electrode360 to the power supply. The active electrode 362 may form a distalportion of shaft 358, or it may also have a connector extending throughshaft 358 to the power supply.

In use, the physician positions active electrode 362 adjacent to thetissue surface to be treated (i.e., a spinal disc). The power supply isactivated to provide an ablation voltage between active and returnelectrodes 362, 360, respectively, and a coagulation or thermal heatingvoltage between coagulation and return electrodes 380, 360,respectively. An electrically conductive fluid can then be providedaround active electrode 362, and in the junction between the active andreturn electrodes 360, 362 to provide a current flow path therebetween.This may be accomplished in a variety of manners, as discussed above.The active electrode 362 is then advanced through the space left by theablated tissue to form a channel in the disc. During ablation, theelectric current between the coagulation and return electrode istypically insufficient to cause any damage to the surface of the tissueas these electrodes pass through the tissue surface into the channelcreated by active electrode 362. Once the physician has formed thechannel to the appropriate depth, he or she will cease advancement ofthe active electrode, and will either hold the instrument in place forapproximately 5 seconds to 30 seconds, or can immediately remove thedistal tip of the instrument from the channel (see detailed discussionof this below). In either event, when the active electrode is no longeradvancing, it will eventually stop ablating tissue.

Prior to entering the channel formed by the active electrode 362, anopen circuit exists between return and coagulation electrodes 360, 380.Once coagulation electrode 380 enters this channel, electric currentwill flow from coagulation electrode 380, through the tissue surroundingthe channel, to return electrode 360. This electric current will heatthe tissue immediately surrounding the channel to coagulate any severedvessels at the surface of the channel. If the physician desires, theinstrument may be held within the channel for a period of time to createa lesion around the channel, as discussed in more detail below.

FIG. 16 illustrates yet another embodiment of an electrosurgical system440 incorporating a dispersive return pad 450 attached to theelectrosurgical probe 400. In this embodiment, the invention functionsin the bipolar mode as described above. In addition, the system 440 mayfunction in a monopolar mode in which a high frequency voltagedifference is applied between the active electrode(s) 410, and thedispersive return pad 450. In the exemplary embodiment, the pad 450 andthe probe 400 are coupled together, and are both disposable, single-useitems. The pad 450 includes an electrical connector 452 that extendsinto handle 404 of probe 400 for direct connection to the power supply.Of course, the invention would also be operable with a standard returnpad that connects directly to the power supply. In this embodiment, thepower supply 460 will include a switch, e.g., a foot pedal 462, forswitching between the monopolar and bipolar modes. In the bipolar mode,the return path on the power supply is coupled to return electrode 408on probe 400, as described above. In the monopolar mode, the return pathon the power supply is coupled to connector 452 of pad 450, activeelectrode(s) 410 are decoupled from the electrical circuit, and returnelectrode 408 functions as the active electrode. This allows the surgeonto switch between bipolar and monopolar modes during, or prior to, thesurgical procedure. In some cases, it may be desirable to operate in themonopolar mode to provide deeper current penetration and, thus, agreater thermal heating of the tissue surrounding the return electrodes.In other cases, such as ablation of tissue, the bipolar modality may bepreferable to limit the current penetration to the tissue.

In one configuration, the dispersive return pad 450 is adapted forcoupling to an external surface of the patient in a region substantiallyclose to the target region. For example, during the treatment of tissuein the head and neck, the dispersive return pad is designed andconstructed for placement in or around the patient's shoulder, upperback or upper chest region. This design limits the current path throughthe patient's body to the head and neck area, which minimizes the damagethat may be generated by unwanted current paths in the patient's body,particularly by limiting current flow through the patient's heart. Thereturn pad is also designed to minimize the current densities at thepad, to thereby minimize patient skin burns in the region where the padis attached.

Referring to FIG. 17, the electrosurgical system according to thepresent invention may also be configured as a catheter system 400. Asshown in FIG. 17, a catheter system 400 generally comprises anelectrosurgical catheter 460 connected to a power supply 28 by aninterconnecting cable 486 for providing high frequency voltage to atarget tissue and an irrigant reservoir or source 600 for providingelectrically conductive fluid to the target site. Catheter 460 generallycomprises an elongate, flexible shaft body 462 including a tissueremoving or ablating region 464 at the distal end of body 462. Theproximal portion of catheter 460 includes a multi-lumen fitment 614which provides for interconnections between lumens and electrical leadswithin catheter 460 and conduits and cables proximal to fitment 614. Byway of example, a catheter electrical connector 496 is removablyconnected to a distal cable connector 494 which, in turn, is removablyconnectable to generator 28 through connector 492. One or moreelectrically conducting lead wires (not shown) within catheter 460extend between one or more active electrodes 463 and a coagulationelectrode 467 at tissue ablating region 464 and one or morecorresponding electrical terminals (also not shown) in catheterconnector 496 via active electrode cable branch 487. Similarly, a returnelectrode 466 at tissue ablating region 464 is coupled to a returnelectrode cable branch 489 of catheter connector 496 by lead wires (notshown). Of course, a single cable branch (not shown) may be used forboth active and return electrodes.

Catheter body 462 may include reinforcing fibers or braids (not shown)in the walls of at least the distal ablation region 464 of body 462 toprovide responsive torque control for rotation of active electrodesduring tissue engagement. This rigid portion of the catheter body 462preferably extends only about 7 mm to 10 mm while the remainder of thecatheter body 462 is flexible to provide good trackability duringadvancement and positioning of the electrodes adjacent target tissue.

In some embodiments, conductive fluid 50 is provided to tissue ablationregion 464 of catheter 460 via a lumen (not shown in FIG. 17) withincatheter 460. Fluid is supplied to the lumen from the source along aconductive fluid supply line 602 and a conduit 603, which is coupled tothe inner catheter lumen at multi-lumen fitment 614. The source ofconductive fluid (e.g., isotonic saline) may be an irrigant pump system(not shown) or a gravity-driven supply, such as an irrigant reservoir600 positioned several feet above the level of the patient and tissueablating region. A control valve 604 may be positioned at the interfaceof fluid supply line 602 and conduit 603 to allow manual control of theflow rate of electrically conductive fluid 50. Alternatively, a meteringpump or flow regulator may be used to precisely control the flow rate ofthe conductive fluid.

System 400 can further include an aspiration or vacuum system (notshown) to aspirate liquids and gases from the target site. Theaspiration system will usually comprise a source of vacuum coupled tofitment 614 by a aspiration connector 605.

The present invention is particularly useful in microendoscopicdiscectomy procedures, e.g., for decompressing a nerve root with alumbar discectomy. As shown in FIGS. 18–23, a percutaneous penetration270 is made in the patients' back 272 so that the superior lamina 274can be accessed. Typically, a small needle (not shown) is used initiallyto localize the disc space level, and a guidewire (not shown) isinserted and advanced under lateral fluoroscopy to the inferior edge ofthe lamina 274. Sequential cannulated dilators 276 are inserted over theguide wire and each other to provide a hole from the incision 220 to thelamina 274. The first dilator may be used to “palpate” the lamina 274,assuring proper location of its tip between the spinous process andfacet complex just above the inferior edge of the lamina 274. As shownin FIG. 21, a tubular retractor 278 is then passed over the largestdilator down to the lamina 274. The dilators 276 are removed,establishing an operating corridor within the tubular retractor 278.

As shown in FIG. 19, an endoscope 280 is then inserted into the tubularretractor 278 and a ring clamp 282 is used to secure the endoscope 280.Typically, the formation of the operating corridor within retractor 278requires the removal of soft tissue, muscle or other types of tissuethat were forced into this corridor as the dilators 276 and retractor278 were advanced down to the lamina 274. This tissue is usually removedwith mechanical instruments, such as pituitary rongeurs, curettes,graspers, cutters, drills, microdebriders, and the like. Unfortunately,these mechanical instruments greatly lengthen and increase thecomplexity of the procedure. In addition, these instruments sever bloodvessels within this tissue, usually causing profuse bleeding thatobstructs the surgeon's view of the target site.

According to another aspect of the present invention, an electrosurgicalprobe or catheter 284 as described above is introduced into theoperating corridor within the retractor 278 to remove the soft tissue,muscle and other obstructions from this corridor so that the surgeon caneasily access and visualization the lamina 274. Once the surgeon hasintroduced the probe 284, electrically conductive fluid 285 can bedelivered through tube 233 and opening 237 to the tissue (see FIG. 4).The fluid flows past the return electrode 112 to the active electrodes104 at the distal end of the shaft. The rate of fluid flow is controlledwith valve 17 (FIG. 1) such that the zone between the tissue andelectrode support 102 is constantly immersed in the fluid. The powersupply 28 is then turned on and adjusted such that a high frequencyvoltage difference is applied between active electrodes 104 and returnelectrode 112. The electrically conductive fluid provides the conductionpath (see current flux lines) between active electrodes 104 and thereturn electrode 112.

The high frequency voltage is sufficient to convert the electricallyconductive fluid (not shown) between the target tissue and activeelectrode(s) 104 into an ionized vapor layer or plasma (not shown). As aresult of the applied voltage difference between active electrode(s) 104and the target tissue (i.e., the voltage gradient across the plasmalayer), charged particles in the plasma (viz., electrons) areaccelerated towards the tissue. At sufficiently high voltagedifferences, these charged particles gain sufficient energy to causedissociation of the molecular bonds within tissue structures. Thismolecular dissociation is accompanied by the volumetric removal (i.e.,ablative sublimation) of tissue and the production of low molecularweight gases, such as oxygen, nitrogen, carbon dioxide, hydrogen andmethane. The short range of the accelerated charged particles within thetissue confines the molecular dissociation process to the surface layerto minimize damage and necrosis to the underlying tissue.

During the process, the gases will be aspirated through opening 209 andsuction tube 211 to a vacuum source. In addition, excess electricallyconductive fluid, and other fluids (e.g., blood) will be aspirated fromthe operating corridor to facilitate the surgeon's view. During ablationof the tissue, the residual heat generated by the current flux lines(typically less than 150° C.), will usually be sufficient to coagulateany severed blood vessels at the site. If not, the surgeon may switchthe power supply 28 into the coagulation mode by lowering the voltage toa level below the threshold for fluid vaporization, as discussed above.This simultaneous hemostasis results in less bleeding and facilitatesthe surgeon's ability to perform the procedure.

Another advantage of the present invention is the ability to preciselyablate soft tissue without causing necrosis or thermal damage to theunderlying and surrounding tissues, nerves or bone. In addition, thevoltage can be controlled so that the energy directed to the target siteis insufficient to ablate the lamina 274 so that the surgeon canliterally clean the tissue off the lamina 274, without ablating orotherwise effecting significant damage to the lamina.

Referring now to FIGS. 20 and 21, once the operating corridor issufficiently cleared, a laminotomy and medial facetectomy isaccomplished either with conventional techniques (e.g., Kerrison punchor a high speed drill) or with the electrosurgical probe 284 asdiscussed above. After the nerve root is identified, medical retractioncan be achieved with a retractor 288, or the present invention can beused to precisely ablate the disc. If necessary, epidural veins arecauterized either automatically or with the coagulation mode of thepresent invention. If an annulotomy is necessary, it can be accomplishedwith a microknife or the ablation mechanism of the present inventionwhile protecting the nerve root with the retractor 288. The herniateddisc 290 is then removed with a pituitary rongeur in a standard fashion,or once again through ablation as described above.

In another embodiment, the present invention involves a channelingtechnique in which small holes or channels are formed within the disc290, and thermal energy is applied to the tissue surface immediatelysurrounding these holes or channels to cause thermal damage to thetissue surface, thereby stiffening and debulking the surrounding tissuestructure of the disc. Applicant has discovered that such stiffening ofthe tissue structure in the disc helps to reduce the pressure appliedagainst the spinal nerves by the disc, thereby relieving back and neckpain.

As shown in FIG. 21, the electrosurgical instrument 350 is introduced tothe target site at the disc 290 as described above, or in anotherpercutaneous manner (see FIGS. 23–25 below). The electrode assembly 351is positioned adjacent to or against the disc surface, and electricallyconductive fluid is delivered to the target site, as described above.Alternatively, the conductive fluid is applied to the target site, orthe distal end of probe 350 is dipped into conductive fluid or gel priorto introducing the probe 350 into the patient. The power supply 28 isthen activated and adjusted such that a high frequency voltagedifference is applied to the electrode assembly as described above.

Depending on the procedure, the surgeon may translate or otherwise movethe electrodes relative to the target disc tissue to form holes,channels, stripes, divots, craters or the like within the disc. Inaddition, the surgeon may purposely create some thermal damage withinthese holes, or channels to form scar tissue that will stiffen anddebulk the disc. In one embodiment, the physician axially translates theelectrode assembly 351 into the disc tissue as the tissue isvolumetrically removed to form one or more holes 702 therein (see alsoFIG. 22). The holes 702 will typically have a diameter of less than 2mm, preferably less than 1 mm. In another embodiment (not shown), thephysician translates the active electrode across the outer surface ofthe disc to form one or more channels or troughs. Applicant has foundthat the present invention can quickly and cleanly create such holes,divots or channels in tissue with the cold ablation technology describedherein. A more complete description of methods for forming holes orchannels in tissue can be found in U.S. Pat. No. 5,683,366, the completedisclosure of which is incorporated herein by reference for allpurposes.

FIG. 22 is a more detailed viewed of the probe 350 of FIG. 15D forming ahole 702 in a disc 290. Hole 702 is preferably formed with the methodsdescribed in detail above. Namely, a high frequency voltage differenceis applied between active and return electrodes 362, 360, respectively,in the presence of an electrically conductive fluid such that anelectric current 361 passes from the active electrode 362, through theconductive fluid, to the return electrode 360. As shown in FIG. 22, thiswill result in shallow or no current penetration into the disc tissue704. The fluid may be delivered to the target site, applied directly tothe target site, or the distal end of the probe may be dipped into thefluid prior to the procedure. The voltage is sufficient to vaporize thefluid around active electrode 362 to form a plasma with sufficientenergy to effect molecular dissociation of the tissue. The distal end ofprobe 350 is then axially advanced through the tissue as the tissue isremoved by the plasma in front of the probe 350. The holes 702 willtypically have a depth D in the range of about 0.5 cm to 2.5 cm,preferably about 1.2 cm to 1.8 cm, and a diameter d of about 0.5 mm to 5mm, preferably about 1.0 mm to 3.0 mm. The exact diameter will, ofcourse, depend on the diameter of the electrosurgical probe used for theprocedure.

During the formation of each hole 702, the conductive fluid betweenactive and return electrodes 362, 360 will generally minimize currentflow into the surrounding tissue, thereby minimizing thermal damage tothe tissue. Therefore, severed blood vessels on the surface 705 of thehole 702 may not be coagulated as the electrodes 362 advance through thetissue. In addition, in some procedures, it may be desired to thermallydamage the surface 705 of the hole 702 to stiffen the tissue. For thesereasons, it may be desired in some procedures to increase the thermaldamage caused to the tissue surrounding hole 702. In the embodimentshown in FIG. 15D, it may be necessary to either: (1) withdraw the probe350 slowly from hole 702 after coagulation electrode 380 has at leastpartially advanced past the outer surface of the disc tissue 704 intothe hole 702 (as shown in FIG. 22); or (2) hold the probe 350 within thehole 702 for a period of time, e.g., on the order of 1 seconds to 30seconds. Once the coagulation electrode is in contact with, or adjacentto, tissue, electric current 755 flows through the tissue surroundinghole 702 and creates thermal damage therein. The coagulation and returnelectrodes 380, 360 both have relatively large, smooth exposed surfacesto minimize high current densities at their surfaces, which minimizesdamage to the surface 705 of hole. Meanwhile, the size and spacing ofthese electrodes 360, 380 allows for relatively deep current penetrationinto the tissue 704. In the representative embodiment, the thermalnecrosis (not shown) will extend about 1.0 mm to 5.0 mm from surface 705of hole 702. In this embodiment, the probe may include one or moretemperature sensors (not shown) on probe coupled to one or moretemperature displays on the power supply 28 such that the physician isaware of the temperature within the hole 702 during the procedure.

In other embodiments, the physician switches the electrosurgical systemfrom the ablation mode to the subablation or thermal heating mode afterthe hole 702 has been formed. This is typically accomplished by pressinga switch or foot pedal to reduce the voltage applied to a level belowthe threshold required for ablation for the particular electrodeconfiguration and the conductive fluid being used in the procedure (asdescribed above). In the subablation mode, the physician will thenremove the distal end of the probe 350 from the hole 702. As the probeis withdrawn, high frequency current flows from the active electrodes362 through the surrounding tissue to the return electrode 360. Thiscurrent flow heats the tissue and coagulates severed blood vessels atsurface 705.

In another embodiment, the electrosurgical probe of the presentinvention can be used to ablate and/or contract soft tissue within thedisc 290 to allow the annulus fibrosus 292 to repair itself to preventreoccurrence of this procedure. For tissue contraction, a sufficientvoltage difference is applied between the active electrodes 104 and thereturn electrode 112 to elevate the tissue temperature from normal bodytemperatures (e.g., 37° C.) to temperatures in the range of 45° C. to90° C., preferably in the range from 60° C. to 70° C. This temperatureelevation causes contraction of the collagen connective fibers withinthe disc tissue so that the nucleus pulposus withdraws into the annulusfibrosus 292.

In one method of tissue contraction according to the present invention,an electrically conductive fluid is delivered to the target site asdescribed above, and heated to a sufficient temperature to inducecontraction or shrinkage of the collagen fibers in the target tissue.The electrically conductive fluid is heated to a temperature sufficientto substantially irreversibly contract the collagen fibers, whichgenerally requires a tissue temperature in the range of about 45° C. to90° C., usually about 60° C. to 70° C. The fluid is heated by applyinghigh frequency electrical energy to the active electrode(s) in contactwith the electrically conductive fluid. The current emanating from theactive electrode(s) 104 heats the fluid and generates a jet or plume ofheated fluid, which is directed towards the target tissue. The heatedfluid elevates the temperature of the collagen sufficiently to causehydrothermal shrinkage of the collagen fibers. The return electrode 112draws the electric current away from the tissue site to limit the depthof penetration of the current into the tissue, thereby inhibitingmolecular dissociation and breakdown of the collagen tissue andminimizing or completely avoiding damage to surrounding and underlyingtissue structures beyond the target tissue site. In an exemplaryembodiment, the active electrode(s) 104 are held away from the tissue asufficient distance such that the RF current does not pass into thetissue at all, but rather passes through the electrically conductivefluid back to the return electrode. In this embodiment, the primarymechanism for imparting energy to the tissue is the heated fluid, ratherthan the electric current.

In an alternative embodiment, the active electrode(s) 104 are broughtinto contact with, or close proximity to, the target tissue so that theelectric current passes directly into the tissue to a selected depth. Inthis embodiment, the return electrode draws the electric current awayfrom the tissue site to limit its depth of penetration into the tissue.Applicant has discovered that the depth of current penetration also canbe varied with the electrosurgical system of the present invention bychanging the frequency of the voltage applied to the active electrodeand the return electrode. This is because the electrical impedance oftissue is known to decrease with increasing frequency due to theelectrical properties of cell membranes which surround electricallyconductive cellular fluid. At lower frequencies (e.g., less than 350kHz), the higher tissue impedance, the presence of the return electrodeand the active electrode configuration of the present invention(discussed in detail below) cause the current flux lines to penetrateless deeply resulting in a smaller depth of tissue heating. In anexemplary embodiment, an operating frequency of about 100 kHz to 200 kHzis applied to the active electrode(s) to obtain shallow depths ofcollagen shrinkage (e.g., usually less than 1.5 mm and preferably lessthan 0.5 mm).

In another aspect of the invention, the size (e.g., diameter orprincipal dimension) of the active electrodes employed for treating thetissue are selected according to the intended depth of tissue treatment.As described previously in copending patent application PCTInternational Application, U.S. National Phase Serial No.PCT/US94/05168, the depth of current penetration into tissue increaseswith increasing dimensions of an individual active electrode (assumingother factors remain constant, such as the frequency of the electriccurrent, the return electrode configuration, etc.). The depth of currentpenetration (which refers to the depth at which the current density issufficient to effect a change in the tissue, such as collagen shrinkage,irreversible necrosis, etc.) is on the order of the active electrodediameter for the bipolar configuration of the present invention andoperating at a frequency of about 100 kHz to about 200 kHz. Accordingly,for applications requiring a smaller depth of current penetration, oneor more active electrodes of smaller dimensions would be selected.Conversely, for applications requiring a greater depth of currentpenetration, one or more active electrodes of larger dimensions would beselected.

FIGS. 23–25 illustrate another system and method for treating swollen orherniated spinal discs according to the present invention. In thisprocedure, an electrosurgical probe 800 comprises a long, thinneedle-like shaft 802 (e.g., on the order of about 1 mm in diameter orless) that can be percutaneously introduced posteriorly through thepatient's back directly into the spine. The shaft 802 may or may not beflexible, depending on the method of access chosen by the physician. Theprobe shaft 802 will include one or more active electrode(s) 804 forapplying electrical energy to tissues within the spine. The probe 800may include one or more return electrode(s) 806, or the return electrodemay be positioned on the patient's back, as a dispersive pad (notshown). As discussed below, however, a bipolar design is preferable.

As shown in FIG. 23, the distal portion of shaft 802 is introducedanteriorly through a small percutaneous penetration into the annulusfibrosus 292 of the target spinal disc. To facilitate this process, thedistal end of shaft 802 may taper down to a sharper point (e.g., aneedle), which can then be retracted to expose active electrode(s) 804.Alternatively, the electrodes may be formed around the surface of thetapered distal portion of shaft (not shown). In either embodiment, thedistal end of shaft is delivered through the annulus 292 to the targetnucleus pulposus 294, which may be herniated, extruded, non-extruded, orsimply swollen. As shown in FIG. 24, high frequency voltage is appliedbetween active electrode(s) 804 and return electrode(s) 806 to heat thesurrounding collagen to suitable temperatures for contraction (i.e.,typically about 55° C. to about 70° C.). As discussed above, thisprocedure may be accomplished with a monopolar configuration, as well.However, applicant has found that the bipolar configuration shown inFIGS. 23–25 provides enhanced control of the high frequency current,which reduces the risk of spinal nerve damage.

As shown in FIGS. 24 and 25, once the nucleus pulposus 294 has beensufficiently contracted to retract from impingement on the nerve 720,the probe 800 is removed from the target site. In the representativeembodiment, the high frequency voltage is applied between active andreturn electrode(s) 804, 806 as the probe is withdrawn through theannulus 292. This voltage is sufficient to cause contraction of thecollagen fibers within the annulus 292, which allows the annulus 292 tocontract around the hole formed by probe 800, thereby improving thehealing of this hole. Thus, the probe 800 seals its own passage as it iswithdrawn from the disc.

FIG. 26A is a side view of an electrosurgical probe 900, according toone embodiment of the invention. Probe 900 includes a shaft 902 having adistal end portion 902 a and a proximal end portion 902 b. An activeelectrode 910 is disposed on distal end portion 902 a. Although only oneactive electrode is shown in FIG. 26A, embodiments including a pluralityof active electrodes are also within the scope of the invention. Probe900 further includes a handle 904 which houses a connection block 906for coupling electrodes, e.g. active electrode 910, thereto. Connectionblock 906 includes a plurality of pins 908 adapted for coupling probe900 to a power supply unit, e.g. power supply 28 (FIG. 1).

FIG. 26B is a side view of the distal end portion of the electrosurgicalprobe of FIG. 26A, showing details of shaft distal end portion 902 a.Distal end portion 902 a includes an insulating collar or spacer 916proximal to active electrode 910, and a return electrode 918 proximal tocollar 916. A first insulating sleeve (FIG. 28B) may be located beneathreturn electrode 918. A second insulating jacket or sleeve 920 mayextend proximally from return electrode 918. Second insulating sleeve920 serves as an electrical insulator to inhibit current flow into theadjacent tissue. In a currently preferred embodiment, probe 900 furtherincludes a shield 922 extending proximally from second insulating sleeve920. Shield 922 may be formed from a conductive metal such as stainlesssteel, and the like. Shield 922 functions to decrease the amount ofleakage current passing from probe 900 to a patient or a user (e.g.,surgeon). In particular, shield 922 decreases the amount of capacitivecoupling between return electrode 918 and an introducer needle 928 (FIG.31A). Typically shield 922 is coupled to an outer floating conductivelayer or cable shield (not shown) of a cable, e.g. cables 22, 34 (FIG.1), connecting probe 900 to power supply 28. In this way, the capacitorbalance of shaft 902 is disturbed. In one embodiment, shield 922 may becoated with a durable, hard compound such as titanium nitride. Such acoating has the advantage of providing reduced friction between shield922 and introducer inner wall 932 as shaft 902 is axially translatedwithin introducer needle 928 (e.g., FIGS. 31A, 31B).

FIG. 27A is a side view of an electrosurgical probe 900 showing a firstcurve 924 and a second curve 926 located at distal end portion 902 a,wherein second curve 926 is proximal to first curve 924. First curve 924and second curve 926 may be separated by a linear (i.e. straight, ornon-curved), or substantially linear, inter-curve portion 925 of shaft902.

FIG. 27B is a side view of shaft distal end portion 902 a within arepresentative introducer device or needle 928 having an inner diameterD. Shaft distal end portion 902 a includes first curve 924 and secondcurve 926 separated by inter-curve portion 925. In one embodiment, shaftdistal end portion 902 a includes a linear or substantially linearproximal portion 901 extending from proximal end portion 902 b to secondcurve 926, a linear or substantially linear inter-curve portion 925between first and second curves 924, 926, and a linear or substantiallylinear distal portion 909 between first curve 924 and the distal tip ofshaft 902 (the distal tip is represented in FIG. 27B as an electrodehead 911). When shaft distal end portion 902 a is located withinintroducer needle 928, first curve 924 subtends a first angle ∀ to theinner surface of needle 928, and second curve 926 subtends a secondangle ∃ to inner surface 932 of needle 928. (In the situation shown inFIG. 27B, needle inner surface 932 is essentially parallel to thelongitudinal axis of shaft proximal end portion 902 b (FIG. 27A).) Inone embodiment, shaft distal end portion 902 a is designed such that theshaft distal tip occupies a substantially central transverse locationwithin the lumen of introducer needle 928 when shaft distal end portion902 a is translated axially with respect to introducer needle 928. Thus,as shaft distal end portion 902 a is advanced through the distal openingof needle 928 (FIGS. 30B, 31B), and then retracted back into the distalopening, the shaft distal tip will always occupy a transverse locationtowards the center of introducer needle 928 (even though the tip may becurved or biased away from the longitudinal axis of shaft 902 and needle928 upon its advancement past the distal opening of introducer needle928). In one embodiment, shaft distal end portion 902 a is flexible andhas a configuration which requires shaft distal end portion 902 a bedistorted in the region of at least second curve 926 by application of alateral force imposed by inner wall 932 of introducer needle 928 asshaft distal end portion 902 a is introduced or retracted into needle928. In one embodiment, first curve 924 and second curve 926 are in thesame plane relative to the longitudinal axis of shaft 902, and first andsecond curves 924, 926 are in opposite directions.

The “S-curve” configuration of shaft 902 shown in FIGS. 27A–C allows thedistal end or tip of a device to be advanced or retracted through needledistal end 928 a and within the lumen of needle 928 without the distalend or tip contacting introducer needle 928. Accordingly, this designallows a sensitive or delicate component to be located at the distal tipof a device, wherein the distal end or tip is advanced or retractedthrough a lumen of an introducer instrument comprising a relatively hardmaterial (e.g., an introducer needle comprising stainless steel). Thisdesign also allows a component located at a distal end or tip of adevice to be constructed from a relatively soft material, and for thecomponent located at the distal end or tip to be passed through anintroducer instrument comprising a hard material without risking damageto the component comprising a relatively soft material.

The “S-curve” design of shaft distal end portion 902 a allows the distaltip (e.g., electrode head 911) to be advanced and retracted through thedistal opening of needle 928 while avoiding contact between the distaltip and the edges of the distal opening of needle 928. (If, for example,shaft distal end portion 902 a included only a single curve the distaltip would ordinarily come into contact with needle distal end 928 a asshaft 902 is retracted into the lumen of needle 928.) In preferredembodiments, the length L2 of distal portion 909 and the angle ∀ betweendistal portion 909 and needle inner surface 932 928, when shaft distalend portion 902 a is compressed within needle 928, are selected suchthat the distal tip is substantially in the center of the lumen ofneedle 928, as shown in FIG. 27B. Thus, as the length L2 increases, theangle ∀ will decrease, and vice versa. The exact values of length L2 andangle ∀ will depend on the inner diameter, D of needle 928, the innerdiameter, d of shaft distal end portion 902 a, and the size of the shaftdistal tip.

The presence of first and second curves, 924, 926 provides a pre-definedbias in shaft 902. In addition, in one embodiment shaft distal endportion 902 a is designed such that at least one of first and secondcurves 924, 926 are compressed to some extent as shaft distal endportion 902 a is retracted into the lumen of needle 928. Accordingly,the angle of at least one of curves 924, 926 may be changed when distalend portion 902 a is advanced out through the distal opening ofintroducer needle 928, as compared with the corresponding angle whenshaft distal end portion is completely retracted within introducerneedle 928. For example, FIG. 27C shows shaft 902 of FIG. 27B free fromintroducer needle 928, wherein first and second curves 924, 926 areallowed to adopt their natural or uncompressed angles ∀′ and ∃′,respectively, wherein ∃′ is typically equal to or greater than ∃. Angle∀′ may be greater than, equal to, or less than angle ∀. Angle ∃′ issubtended by inter-curve portion 925 and proximal portion 901. Whenshaft distal end portion 902 a is unrestrained by introducer needle 928,proximal portion 901 approximates the longitudinal axis of shaft 902.Angle ∀′ is subtended between linear distal portion 909 and a line drawnparallel to proximal portion 901. Electrode head 911 is omitted fromFIG. 27C for the sake of clarity.

The principle described above with reference to shaft 902 and introducerneedle 928 may equally apply to a range of other medical devices. Thatis to say, the “S-curve” configuration of the invention may be includedas a feature of any medical system or apparatus in which a medicalinstrument may be axially translated or passed within an introducerdevice. In particular, the principle of the “S-curve” configuration ofthe invention may be applied to any apparatus wherein it is desired thatthe distal end of the medical instrument does not contact or impingeupon the introducer device as the medical instrument is advanced from orretracted into the introducer device. The introducer device may be anyapparatus through which a medical instrument is passed. Such medicalsystems may include, for example, a catheter, a cannula, an endoscope,and the like.

When shaft 902 is advanced distally through the needle lumen to a pointwhere second curve 926 is located distal to needle distal end 928 a, theshaft distal tip is deflected from the longitudinal axis of needle 928.The amount of this deflection is determined by the relative size ofangles ∃′ and ∀′, and the relative lengths of L1 and L2. The amount ofthis deflection will in turn determine the size of a channel or lesion(depending on the application) formed in a tissue treated by electrodehead 911 when shaft 902 is rotated circumferentially with respect to thelongitudinal axis of probe 900.

As a result of the pre-defined bias in shaft 902, shaft distal endportion 902 a will contact a larger volume of tissue than a linear shafthaving the same dimensions. In addition, in one embodiment thepre-defined bias of shaft 902 allows the physician to guide or steer thedistal tip of shaft 902 by a combination of axial movement of needledistal end 928 a and the inherent curvature at shaft distal end portion902 a of probe 900.

Shaft 902 preferably has a length in the range of from about 4 to 30 cm.In one aspect of the invention, probe 900 is manufactured in a range ofsizes having different lengths and/or diameters of shaft 902. A shaft ofappropriate size can then be selected by the surgeon according to thebody structure or tissue to be treated and the age or size of thepatient. In this way, patients varying in size from small children tolarge adults can be accommodated. Similarly, for a patient of a givensize, a shaft of appropriate size can be selected by the surgeondepending on the organ or tissue to be treated, for example, whether anintervertebral disc to be treated is in the lumbar spine or the cervicalspine. For example, a shaft suitable for treatment of a disc of thecervical spine may be substantially smaller than a shaft for treatmentof a lumbar disc. For treatment of a lumbar disc in an adult, shaft 902is preferably in the range of from about 15 to 25 cm. For treatment of acervical disc, shaft 902 is preferably in the range of from about 4 toabout 15 cm.

The diameter of shaft 902 is preferably in the range of from about 0.5to about 2.5 mm, and more preferably from about 1 to 1.5 mm. First curve924 is characterized by a length L1, while second curve 926 ischaracterized by a length L2 (FIG. 27B). Inter-curve portion 925 ischaracterized by a length L3, while shaft 902 extends distally fromfirst curve 924 a length L4. In one embodiment, L2 is greater than L1.Length L1 may be in the range of from about 0.5 to about 5 mm, while L2may be in the range of from about 1 to about 10 mm. Preferably, L3 andL4 are each in the range of from about 1 to 6 mm.

FIG. 28A is a side view of shaft distal end portion 902 a ofelectrosurgical probe 900 showing a head 911 of active electrode 910(the latter not shown in FIG. 28A), according to one embodiment of theinvention. In this embodiment, electrode head 911 includes an apicalspike 911 a and an equatorial cusp 911 b. Electrode head 911 exhibits anumber of advantages as compared with, for example, an electrosurgicalprobe having a blunt, globular, or substantially spherical activeelectrode. In particular, electrode head 911 provides a high currentdensity at apical spike 911 a and cusp 911 b. In turn, high currentdensity in the vicinity of an active electrode is advantageous in thegeneration of a plasma; and, as is described fully hereinabove,generation of a plasma in the vicinity of an active electrode isfundamental to ablation of tissue with minimal collateral thermal damageaccording to certain embodiments of the instant invention. Electrodehead 911 provides an additional advantage, in that the sharp edges ofcusp 911 b, and more particularly of apical spike 911 a, facilitatemovement and guiding of head 911 into tissue during surgical procedures,as described fully hereinbelow. In contrast, an electrosurgical probehaving a blunt or rounded apical electrode is more likely to follow apath of least resistance, such as a channel which was previously ablatedwithin nucleus pulposus tissue. Although certain embodiments of theinvention depict head 911 as having a single apical spike, other shapesfor the apical portion of active electrode 910 are also within the scopeof the invention.

FIG. 28B is a longitudinal cross-sectional view of distal end portion902 a of shaft 902. Apical electrode head 911 is in communication with afilament 912. Filament 912 typically comprises an electricallyconductive wire encased within a first insulating sleeve 914. Firstinsulating sleeve 914 comprises an insulator, such as various syntheticpolymeric materials. An exemplary material from which first insulatingsleeve 914 may be constructed is a polyimide. First insulating sleeve914 may extend the entire length of shaft 902 proximal to head 911. Aninsulating collar or spacer 916 is disposed on the distal end of firstinsulating sleeve 914, adjacent to electrode head 911. Collar 916preferably comprises a material such as a glass, a ceramic, or silicone.The exposed portion of first insulating sleeve 914 (i.e., the portionproximal to collar 916) is encased within a cylindrical return electrode918. Return electrode 918 may extend proximally the entire length ofshaft 902. Return electrode 918 may comprise an electrically conductivematerial such as stainless steel, tungsten, platinum or its alloys,titanium or its alloys, molybdenum or its alloys, nickel or its alloys,and the like. A proximal portion of return electrode 918 is encasedwithin a second insulating sleeve 920, so as to provide an exposed bandof return electrode 918 located distal to second sleeve 920 and proximalto collar 916. Second sleeve 920 provides an insulated portion of shaft920 which facilitates handling of probe 900 by the surgeon during asurgical procedure. A proximal portion of second sleeve 920 is encasedwithin an electrically conductive shield 922. Second sleeve 920 andshield 922 may also extend proximally for the entire length of shaft902.

FIG. 29 is a side view of shaft distal end portion 902 a ofelectrosurgical probe 900, indicating the position of first and secondcurves 924, 926, respectively. Probe 900 includes head 911, collar 916,return electrode 918, second insulating sleeve 920, and shield 922,generally as described with reference to FIGS. 28A, 28B. In theembodiment of FIG. 29, first curve 924 is located within returnelectrode 918, while second curve 926 is located within shield 922.However, according to various embodiments of the invention, shaft 902may be provided in which one or more curves are present at alternativeor additional locations or components of shaft 902, other than thelocation of first and second curves 924, 926, respectively, shown inFIG. 29.

FIG. 30A shows distal end portion 902 a of shaft 902 extended distallyfrom an introducer needle 928, according to one embodiment of theinvention. Introducer needle 928 may be used to conveniently introduceshaft 902 into tissue, such as the nucleus pulposus of an intervertebraldisc. In this embodiment, due to the curvature of shaft distal end 902a, when shaft 902 is extended distally beyond introducer needle 928,head 911 is displaced laterally from the longitudinal axis of introducerneedle 928. However, as shown in FIG. 30B, as shaft 902 is retractedinto introducer needle 928, head 911 assumes a substantially centraltransverse location within lumen 930 (see also FIG. 31B) of introducer928. Such re-alignment of head 911 with the longitudinal axis ofintroducer 928 is achieved by specific design of the curvature of shaftdistal end 902 a, as accomplished by the instant inventors. In thismanner, contact of various components of shaft distal end 902 a (e.g.,electrode head 911, collar 916, return electrode 918) is prevented,thereby not only facilitating extension and retraction of shaft 902within introducer 928, but also avoiding a potential source of damage tosensitive components of shaft 902.

FIG. 31A shows a side view of shaft 902 in relation to an inner wall 932of introducer needle 928 upon extension or retraction of electrode head911 from, or within, introducer needle 928. Shaft 902 is located withinintroducer 928 with head 911 adjacent to introducer distal end 928 a(FIG. 31B). Under these circumstances, curvature of shaft 902 may causeshaft distal end 902 a to be forced into contact with introducer innerwall 932, e.g., at a location of second curve 926. Nevertheless, due tothe overall curvature of shaft 902, and in particular the nature andposition of first curve 924 (FIGS. 27A–B), head 911 does not contactintroducer distal end 928 a.

FIG. 31B shows an end view of electrode head 911 in relation tointroducer needle 928 at a point during extension or retraction of shaft902, wherein head 911 is adjacent to introducer distal end 928 a (FIGS.30B, 31B). In this situation, head 911 is substantially centrallypositioned within lumen 930 of introducer 928. Therefore, contactbetween head 911 and introducer 928 is avoided, allowing shaft distalend 902 a to be extended and retracted repeatedly without sustaining anydamage to shaft 902.

FIG. 32A shows shaft proximal end portion 902 b of electrosurgical probe900, wherein shaft 902 includes a plurality of depth markings 903 (shownas 903 a–f in FIG. 32A). In other embodiments, other numbers andarrangements of depth markings 903 may be included on shaft 902. Forexample, in certain embodiments, depth markings may be present along theentire length of shield 922, or a single depth marking 903 may bepresent at shaft proximal end portion 902 b. Depth markings serve toindicate to the surgeon the depth of penetration of shaft 902 into apatient's tissue, organ, or body, during a surgical procedure. Depthmarkings 903 may be formed directly in or on shield 922, and maycomprise the same material as shield 922. Alternatively, depth markings903 may be formed from a material other than that of shield 922. Forexample, depth markings may be formed from materials which have adifferent color and/or a different level of radiopacity, as comparedwith material of shield 922. For example, depth markings may comprise ametal, such as tungsten, gold, or platinum oxide (black), having a levelof radiopacity different from that of shield 922. Such depth markingsmay be visualized by the surgeon during a procedure performed underfluoroscopy. In one embodiment, the length of the introducer needle andthe shaft 902 are selected to limit the range of the shaft beyond thedistal tip of the introducer needle.

FIG. 32B shows a probe 900, wherein shaft 902 includes a mechanical stop905. Preferably, mechanical stop 905 is located at shaft proximal endportion 902 b. Mechanical stop 905 limits the distance to which shaftdistal end 902 a can be advanced through introducer 928 by makingmechanical contact with a proximal end 928 b of introducer 928.Mechanical stop 905 may be a rigid material or structure affixed to, orintegral with, shaft 902. Mechanical stop 905 also serves to monitor thedepth or distance of advancement of shaft distal end 902 a throughintroducer 928, and the degree of penetration of distal end 902 a into apatient's tissue, organ, or body. In one embodiment, mechanical stop 905is movable on shaft 902, and stop 905 includes a stop adjustment unit907 for adjusting the position of stop 905 and for locking stop 905 at aselected location on shaft 902.

FIG. 33 illustrates stages in manufacture of an active electrode 910 ofa shaft 902, according to one embodiment of the present invention. Stage33-I shows an elongated piece of electrically conductive material 912′,e.g., a metal wire, as is well known in the art. Material 912′ includesa first end 912′a and a second end 912′b. Stage 33-II shows theformation of a globular structure 911′ from first end 912′a, whereinglobular structure 911′ is attached to filament 912. Globular structure911′ may be conveniently formed by applying heat to first end 912′a.Techniques for applying heat to the end of a metal wire are well knownin the art. Stage 33-III shows the formation of an electrode head 911from globular structure 911′, wherein active electrode 910 compriseshead 911 and filament 912 attached to head 911. In this particularembodiment, head 911 includes an apical spike 911 a and a substantiallyequatorial cusp 911 b.

FIG. 34 schematically represents a series of steps involved in a methodof making a shaft according to one embodiment of the present invention,wherein step 1000 involves providing an active electrode having afilament, the active electrode including an electrode head attached tothe filament. An exemplary active electrode to be provided in step 1000is an electrode of the type described with reference to FIG. 33. At thisstage (step 1000), the filament may be trimmed to an appropriate lengthfor subsequent coupling to a connection block (FIG. 26A).

Step 1002 involves covering or encasing the filament with a firstinsulating sleeve of an electrically insulating material such as asynthetic polymer or plastic, e.g., a polyimide. Preferably, the firstinsulating sleeve extends the entire length of the shaft. Step 1004involves positioning a collar of an electrically insulating material onthe distal end of the first insulating sleeve, wherein the collar islocated adjacent to the electrode head. The collar is preferably amaterial such as a glass, a ceramic, or silicone. Step 1006 involvesplacing a cylindrical return electrode over the first insulating sleeve.Preferably, the return electrode is positioned such that its distal endis contiguous with the proximal end of the collar, and the returnelectrode preferably extends proximally for the entire length of theshaft. The return electrode may be constructed from stainless steel orother non-corrosive, electrically conductive metal.

According to one embodiment, a metal cylindrical return electrode ispre-bent to include a curve within its distal region (i.e. the returnelectrode component is bent prior to assembly onto the shaft). As aresult, the shaft assumes a first curve upon placing the returnelectrode over the first insulating sleeve, i.e. the first curve in theshaft results from the bend in the return electrode. Step 1008 involvescovering a portion of the return electrode with a second insulatinglayer or sleeve such that a band of the return electrode is exposeddistal to the distal end of the second insulating sleeve. In oneembodiment, the second insulating sleeve comprises a heat-shrink plasticmaterial which is heated prior to positioning the second insulatingsleeve over the return electrode. According to one embodiment, thesecond insulating sleeve is initially placed over the entire length ofthe shaft, and thereafter the distal end of the second insulating sleeveis cut back to expose an appropriate length of the return electrode.Step 1010 involves encasing a proximal portion of the second insulatingsleeve within a shield of electrically conductive material, such as acylinder of stainless steel or other metal, as previously describedherein.

FIG. 35 schematically represents a series of steps involved in a methodof making an electrosurgical probe of the present invention, whereinstep 1100 involves providing a shaft having at least one activeelectrode and at least one return electrode. An exemplary shaft to beprovided in step 1100 is that prepared according to the method describedhereinabove with reference to FIG. 34, i.e., the shaft includes a firstcurve. Step 1102 involves bending the shaft to form a second curve.Preferably, the second curve is located at the distal end portion of theshaft, but proximal to the first curve. In one embodiment, the secondcurve is greater than the first curve. (Features of both the first curveand second curve have been described hereinabove, e.g., with referenceto FIG. 27B.) Step 1104 involves providing a handle for the probe. Thehandle includes a connection block for electrically coupling theelectrodes thereto. Step 1106 involves coupling the active and returnelectrodes of the shaft to the connection block. The connection blockallows for convenient coupling of the electrosurgical probe to a powersupply (e.g., power supply 28, FIG. 1). Thereafter, step 1108 involvesaffixing the shaft to the handle.

FIG. 36A schematically represents a normal intervertebral disc 290 inrelation to the spinal cord 720, the intervertebral disc having an outerannulus fibrosus 292 enclosing an inner nucleus pulposus 294. Thenucleus pulposus is a relatively soft tissue comprising proteins andhaving a relatively high water content, as compared with the harder,more fibrous annulus fibrosus. FIGS. 36B–D each schematically representan intervertebral disc having a disorder which can lead to discogenicpain, for example due to compression of a nerve root by a distortedannulus fibrosus. Thus, FIG. 36B schematically represents anintervertebral disc exhibiting a protrusion of the nucleus pulposus anda concomitant distortion of the annulus fibrosus. The condition depictedin FIG. 36B clearly represents a contained herniation, which can resultin severe and often debilitating pain. FIG. 36C schematically representsan intervertebral disc exhibiting a plurality of fissures within theannulus fibrosus, again with concomitant distortion of the annulusfibrosus. Such annular fissures may be caused by excessive pressureexerted by the nucleus pulposus on the annulus fibrosus. Excessivepressure within the nucleus pulposus tends to intensify disc disordersassociated with the presence of such fissures. FIG. 36D schematicallyrepresents an intervertebral disc exhibiting fragmentation of thenucleus pulposus and a concomitant distortion of the annulus fibrosus.In this situation, over time, errant fragment 294′ of the nucleuspulposus tends to dehydrate and to diminish in size, often leading to adecrease in discogenic pain over an extended period of time (e.g.,several months). For the sake of clarity, each FIGS. 36B, 36C, 36D showsa single disorder. However, in practice more than one of the depicteddisorders may occur in the same disc.

Many patients suffer from discogenic pain resulting, for example, fromconditions of the type depicted in FIGS. 36B–D. However, only a smallpercentage of such patients undergo laminotomy or discectomy. Presently,there is a need for interventional treatment for the large group ofpatients who ultimately do not undergo major spinal surgery, but whosustain significant disability due to various disorders or abnormalitiesof an intervertebral disc. A common disorder of intervertebral discs isa contained herniation in which the nucleus pulposus does not breach theannulus fibrosus, but a protrusion of the disc causes compression of theexiting nerve root, leading to radicular pain. Typical symptoms are legpain compatible with sciatica. Such radicular pain may be considered asa particular form of discogenic pain. Most commonly, containedherniations leading to radicular pain are associated with the lumbarspine, and in particular with intervertebral discs at either L4-5 orL5-S1. Various disc abnormalities are also encountered in the cervicalspine. Methods and apparatus of the invention are applicable to allsegments of the spine, including the cervical spine and the lumbarspine.

FIG. 37 schematically represents shaft 902 of probe 900 inserted withina nucleus pulposus of a disc having at least one fissure in the annulus.Shaft 902 may be conveniently inserted within the nucleus pulposus viaintroducer needle 928 in a minimally invasive percutaneous procedure. Ina preferred embodiment, a disc in the lumbar spine may be accessed via aposterior lateral approach, although other approaches are possible andare within the scope of the invention. The preferred length and diameterof shaft 902 and introducer needle 928 to be used in a procedure willdepend on a number of factors, including the region of the spine (e.g.,lumbar, cervical) or other body region to be treated, and the size ofthe patient. Preferred ranges for shaft 902 are given elsewhere herein.In one embodiment for treatment of a lumbar disc, introducer needle 928preferably has a diameter in the range of from about 50% to 150% theinside diameter of a 17 Gauge needle. In an embodiment for treatment ofa cervical disc, introducer needle 928 preferably has a diameter in therange of from about 50% to 150% the inner diameter of a 20 Gauge needle.

Shaft 902 includes an active electrode 910, as described hereinabove.Shaft 902 features curvature at distal end 902 a/902′a, for example, asdescribed with reference to FIGS. 27A–B. By rotating shaft 902 throughapproximately 180°, shaft distal end 902 a can be moved to a positionindicated by the dashed lines and labeled as 902′a. Thereafter, rotationof shaft 902 through an additional 180° defines a substantiallycylindrical three-dimensional space with a proximal conical arearepresented as a hatched area (shown between 902 a and 902′a). Thebi-directional arrow distal to active electrode 910 indicatestranslation of shaft 902 substantially along the longitudinal axis ofshaft 902. By a combination of axial and rotational movement of shaft902, a much larger volume of the nucleus pulposus can be contacted byelectrode 910, as compared with a corresponding probe having a linear(non-curved) shaft. Furthermore, the curved nature of shaft 902 allowsthe surgeon to change the direction of advancement of shaft 902 byappropriate rotation thereof, and to guide shaft distal end 902 a to aparticular target site within the nucleus pulposus.

It is to be understood that according to certain embodiments of theinvention, the curvature of shaft 902 is the same, or substantially thesame, both prior to it being used in a surgical procedure and while itis performing ablation during a procedure, e.g., within anintervertebral disc. (One apparent exception to this statement, relatesto the stage in a procedure wherein shaft 902 may be transiently“molded” into a somewhat more linear configuration by the constraints ofintroducer inner wall 932 during housing, or passing, of shaft 902within introducer 928.) In contrast, certain prior art devices, andembodiments of the invention to be described hereinbelow (e.g., withreference to FIGS. 43A, 43B), may be linear or lacking a naturallydefined configuration prior to use, and then be steered into a selectedconfiguration during a surgical procedure.

While shaft distal end 902 a is at or adjacent to a target site withinthe nucleus pulposus, probe 900 may be used to ablate tissue byapplication of a first high frequency voltage between active electrode910 and return electrode 918 (e.g., FIG. 26B), wherein the volume of thenucleus pulposus is decreased, the pressure exerted by the nucleuspulposus on the annulus fibrosus is decreased, and at least one nerve ornerve root is decompressed. Accordingly, discogenic pain experienced bythe patient may be alleviated. Preferably, application of the first highfrequency voltage results in formation of a plasma in the vicinity ofactive electrode 910, and the plasma causes ablation by breaking downhigh molecular weight disc tissue components (e.g., proteins) into lowmolecular weight gaseous materials. Such low molecular weight gaseousmaterials may be at least partially vented or exhausted from the disc,e.g., by piston action, upon removal of shaft 902 and introducer 928from the disc and the clearance between the introducer 928 and the shaft902. In addition, by-products of tissue ablation may be removed by anaspiration device (not shown in FIG. 37), as is well known in the art.In this manner, the volume and/or mass of the nucleus pulposus may bedecreased.

In order to initiate and/or maintain a plasma in the vicinity of activeelectrode 910, a quantity of an electrically conductive fluid may beapplied to shaft 902 and/or the tissue to ablated. The electricallyconductive fluid may be applied to shaft 902 and/or to the tissue to beablated, either before or during application of the first high frequencyvoltage. Examples of electrically conductive fluids are saline (e.g.,isotonic saline), and an electrically conductive gel. An electricallyconductive fluid may be applied to the tissue to be ablated before orduring ablation. A fluid delivery unit or device may be a component ofthe electrosurgical probe itself, or may comprise a separate device,e.g., ancillary device 940 (FIG. 41). Alternatively, many body fluidsand/or tissues (e.g., the nucleus pulposus, blood) at the site to beablated are electrically conductive and can participate in initiation ormaintenance of a plasma in the vicinity of the active electrode.

In one embodiment, after ablation of nucleus pulposus tissue by theapplication of the first high frequency voltage and formation of acavity or channel within the nucleus pulposus, a second high frequencyvoltage may be applied between active electrode 910 and return electrode918, wherein application of the second high frequency voltage causescoagulation of nucleus pulposus tissue adjacent to the cavity orchannel. Such coagulation of nucleus pulposus tissue may lead toincreased stiffness, strength, and/or rigidity within certain regions ofthe nucleus pulposus, concomitant with an alleviation of discogenicpain. Furthermore, coagulation of tissues may lead to necrotic tissuewhich is subsequently broken down as part of a natural bodily processand expelled from the body, thereby resulting in de-bulking of the disc.Although FIG. 37 depicts a disc having fissures within the annulusfibrosus, it is to be understood that apparatus and methods of theinvention discussed with reference to FIG. 37 are also applicable totreating other types of disc disorders, including those described withreference to FIGS. 36B, 36D.

FIG. 38 shows shaft 902 of electrosurgical probe 900 within anintervertebral disc, wherein shaft distal end 902 a is targeted to aspecific site within the disc. In the situation depicted in FIG. 38, thetarget site is occupied by an errant fragment 294′ of nucleus pulposustissue. Shaft distal end 902 may be guided or directed, at least inpart, by appropriate placement of introducer 928, such that activeelectrode 910 is in the vicinity of fragment 294′. Preferably, activeelectrode 910 is adjacent to, or in contact with, fragment 294′.Although FIG. 38 depicts a disc in which a fragment of nucleus pulposusis targeted by shaft 902, the invention described with reference to FIG.38 may also be used for targeting other aberrant structures within anintervertebral disc, including annular fissures and containedherniations. In a currently preferred embodiment, shaft 902 includes atleast one curve (not shown in FIG. 38), and other features describedherein with reference to FIGS. 26A-35, wherein shaft distal end 902 amay be precisely guided by an appropriate combination of axial androtational movement of shaft 902. The procedure illustrated in FIG. 38may be performed generally according to the description presented withreference to FIG. 37. That is, shaft 902 is introduced into the disc viaintroducer 928 in a percutaneous procedure. After shaft distal end 902 ahas been guided to a target site, tissue at or adjacent to that site isablated by application of a first high frequency voltage. Thereafter,depending on the particular condition of the disc being treated, asecond high frequency voltage may optionally be applied in order tolocally coagulate tissue within the disc.

FIG. 39 schematically represents a series of steps involved in a methodof ablating disc tissue according to the present invention; wherein step1200 involves advancing an introducer needle towards an intervertebraldisc to be treated. The introducer needle has a lumen having a diametergreater than the diameter of the shaft distal end, thereby allowing freepassage of the shaft distal end through the lumen of the introducerneedle. In one embodiment, the introducer needle preferably has a lengthin the range of from about 3 cm to about 25 cm, and the lumen of theintroducer needle preferably has a diameter in the range of from about0.5 cm. to about 2.5 mm. Preferably, the lumen of the introducer needlehas a diameter in the range of from about 105% to about 500% of thediameter of the shaft distal end. The introducer needle may be insertedin the intervertebral disc percutaneously, e.g. via a posterior lateralapproach. In one embodiment, the introducer needle may have dimensionssimilar to those of an epidural needle, the latter well known in theart.

Optional step 1202 involves introducing an electrically conductivefluid, such as saline, into the disc. In one embodiment, in lieu of step1202, the ablation procedure may rely on the electrical conductivity ofthe nucleus pulposus itself. Step 1204 involves inserting the shaft ofthe electrosurgical probe into the disc, e.g., via the introducerneedle, wherein the distal end portion of the shaft bears an activeelectrode and a return electrode. In one embodiment, the shaft includesan outer shield, first and second curves at the distal end portion ofthe shaft, and an electrode head having an apical spike, generally asdescribed with reference to FIGS. 26A–32.

Step 1206 involves ablating at least a portion of disc tissue byapplication of a first high frequency voltage between the activeelectrode and the return electrode. In particular, ablation of nucleuspulposus tissue according to methods of the invention serves to decreasethe volume of the nucleus pulposus, thereby relieving pressure exertedon the annulus fibrosus, with concomitant decompression of a previouslycompressed nerve root, and alleviation of discogenic pain.

In one embodiment, the introducer needle is advanced towards theintervertebral disc until it penetrates the annulus fibrosus and entersthe nucleus pulposus. The shaft distal end in introduced into thenucleus pulposus, and a portion of the nucleus pulposus is ablated.These and other stages of the procedure may be performed underfluoroscopy to allow visualization of the relative location of theintroducer needle and shaft relative to the nucleus pulposus of thedisc. Additionally or alternatively, the surgeon may introduce theintroducer needle into the nucleus pulposus from a first side of thedisc, then advance the shaft distal end through the nucleus pulposusuntil resistance to axial translation of the electrosurgical probe isencountered by the surgeon. Such resistance may be interpreted by thesurgeon as the shaft distal end having contacted the annulus fibrosus atthe opposite side of the disc. Then, by use of depth markings on theshaft (FIG. 32A), the surgeon can retract the shaft a defined distancein order to position the shaft distal end at a desired location relativeto the nucleus pulposus. Once the shaft distal end is suitablypositioned, high frequency voltage may be applied to the probe via thepower supply unit.

After step 1206, optional step 1208 involves coagulating at least aportion of the disc tissue. In one embodiment, step 1206 results in theformation of a channel or cavity within the nucleus pulposus.Thereafter, tissue at the surface of the channel may be coagulatedduring step 1208. Coagulation of disc tissue may be performed byapplication of a second high frequency voltage, as describedhereinabove. After step 1206 or step 1208, the shaft may be moved (step1210) such that the shaft distal end contacts fresh tissue of thenucleus pulposus. The shaft may be axially translated (i.e. moved in thedirection of its longitudinal axis), may be rotated about itslongitudinal axis, or may be moved by a combination of axial androtational movement. In the latter case, a substantially spiral path isdefined by the shaft distal end. After step 1210, steps 1206 and 1208may be repeated with respect to the fresh tissue of the nucleus pulposuscontacted by the shaft distal end. Alternatively, after step 1206 orstep 1208, the shaft may be withdrawn from the disc (step 1212). Step1214 involves withdrawing the introducer needle from the disc. In oneembodiment, the shaft and the needle may be withdrawn from the discconcurrently. Withdrawal of the shaft from the disc may facilitateexhaustion of ablation by-products from the disc. Such ablationby-products include low molecular weight gaseous compounds derived frommolecular dissociation of disc tissue components, as describedhereinabove. The above method may be used to treat any disc disorder inwhich Coblation® and or coagulation of disc tissue is indicated,including contained herniations. In one embodiment, an introducer needlemay be introduced generally as described for step 1200, and afluoroscopic fluid may be introduced through the lumen of the introducerneedle for the purpose of visualizing and diagnosing a disc abnormalityor disorder. Thereafter, depending on the diagnosis, a treatmentprocedure may be performed, e.g., according to steps 1202 through 1214,using the same introducer needle as access. In one embodiment, a distalportion, or the entire length, of the introducer needle may have aninsulating coating on its external surface. Such an insulating coatingon the introducer needle may prevent interference between theelectrically conductive introducer needle and electrode(s) on the probe.

The size of the cavity or channel formed in a tissue by a singlestraight pass of the shaft through the tissue to be ablated is afunction of the diameter of the shaft (e.g., the diameter of the shaftdistal end and active electrode) and the amount of axial translation ofthe shaft. (By a “single straight pass” of the shaft is meant one axialtranslation of the shaft in a distal direction through the tissue, inthe absence of rotation of the shaft about the longitudinal axis of theshaft, with the power from the power supply turned on.) In the case of acurved shaft, according to various embodiments of the instant invention,a larger channel can be formed by rotating the shaft as it is advancedthrough the tissue. The size of a channel formed in a tissue by a singlerotational pass of the shaft through the tissue to be ablated is afunction of the deflection of the shaft, and the amount of rotation ofthe shaft about its longitudinal axis, as well as the diameter of theshaft (e.g., the diameter of the shaft distal end and active electrode)and the amount of axial translation of the shaft. (By a “singlerotational pass” of the shaft is meant one axial translation of theshaft in a distal direction through the tissue, in the presence ofrotation of the shaft about the longitudinal axis of the shaft, with thepower from the power supply turned on.) To a large extent, the diameterof a channel formed during a rotational pass of the shaft through tissuecan be controlled by the amount of rotation of the shaft, wherein the“amount of rotation” encompasses both the rate of rotation (e.g., theangular velocity of the shaft), and the number of degrees through whichthe shaft is rotated (e.g. the number of turns) per unit length of axialmovement. Typically, according to the invention, the amount of axialtranslation per pass (for either a straight pass or a rotational pass)is not limited by the length of the shaft. Instead, the amount of axialtranslation per single pass is preferably determined by the size of thetissue to be ablated. Depending on the size of the disc or other tissueto be treated, and the nature of the treatment, etc., a channel formedby a probe of the instant invention may preferably have a length in therange of from about 2 mm to about 50 mm, and a diameter in the range offrom about 0.5 mm to about 7.5 mm. In comparison, a channel formed by ashaft of the instant invention during a single rotational pass maypreferably have a diameter in the range of from about 1.5 mm to about 25mm.

A channel formed by a shaft of the instant invention during a singlestraight pass may preferably have a volume in the range of from about 1mm³, or less, to about 2,500 mm³. More preferably, a channel formed by astraight pass of a shaft of the instant invention has a volume in therange of from about 10 mm³ to about 2,500 mm³, and more preferably inthe range of from about 50 mm³ to about 2,500 mm³. In comparison, achannel formed by a shaft of the instant invention during a singlerotational pass typically has a volume from about twice to about 15times the volume of a channel of the same length formed during a singlerotational pass, i.e., in the range of from about 2 mm³ to about 4,000mm³, more preferably in the range of from about 50 mm³ to about 2,000mm³. While not being bound by theory, the reduction in volume of a dischaving one or more channels therein is a function of the total volume ofthe one or more channels. FIG. 40 schematically represents a series ofsteps involved in a method of guiding the distal end of a shaft of anelectrosurgical probe to a target site within an intervertebral disc forablation of specifically targeted disc tissue, wherein steps 1300 and1302 are analogous to steps 1200 and 1204 of FIG. 39. Thereafter step1304 involves guiding the shaft distal end to a defined region withinthe disc. The specific target site may be pre-defined as a result of aprevious procedure to visualize the disc and its abnormality, e.g., viaX-ray examination, endoscopically, or fluoroscopically. As an example, adefined target site within a disc may comprise a fragment of the nucleuspulposus that has migrated within the annulus fibrosus (see, e.g., FIG.36D) resulting in discogenic pain. However, guiding the shaft to definedsites associated with other types of disc disorders are also possibleand is within the scope of the invention.

Guiding the shaft distal end to the defined target site may be performedby axial and/or rotational movement of a curved shaft, as describedhereinabove. Or the shaft may be steerable, for example, by means of aguide wire, as is well known in the art. Guiding the shaft distal endmay be performed during visualization of the location of the shaftrelative to the disc, wherein the visualization may be performedendoscopically or via fluoroscopy. Endoscopic examination may employ afiber optic cable (not shown). The fiber optic cable may be integralwith the electrosurgical probe, or be part of a separate instrument(endoscope). Step 1306 involves ablating disc tissue, and is analogousto step 1206 (FIG. 39). Before or during step 1306, an electricallyconductive fluid may be applied to the disc tissue and/or the shaft inorder to provide a path for current flow between active and returnelectrodes on the shaft, and to facilitate and/or maintain a plasma inthe vicinity of the distal end portion of the shaft. After the shaftdistal end has been guided to a target site and tissue at that site hasbeen ablated, the shaft may be moved locally, e.g., within the sameregion of the nucleus pulposus, or to a second defined target sitewithin the same disc. The shaft distal end may be moved as describedherein (e.g., with reference to step 1210, FIG. 39). Or, according to analternative embodiment, the shaft may be steerable, e.g., by techniqueswell known in the art. Steps 1310 and 1312 are analogous to steps 1212and 1214, respectively (described with reference to FIG. 39).

It is known in the art that epidural steroid injections can transientlydiminish perineural inflammation of an affected nerve root, leading toalleviation of discogenic pain. In one embodiment of the invention,methods for ablation of disc tissue described hereinabove may beconveniently performed in conjunction with an epidural steroidinjection. For example, ablation of disc tissue and epidural injectioncould be carried out as part of a single procedure, by the same surgeon,using equipment common to both procedures (e.g. visualizationequipment). Combining Coblation® and epidural injection in a singleprocedure may provide substantial cost-savings to the healthcareindustry, as well as a significant improvement in patient care.

As alluded to hereinabove, methods and apparatus of the presentinvention can be used to accelerate the healing process ofintervertebral discs having fissures and/or contained herniations. Inone method, the present invention is useful in microendoscopicdiscectomy procedures, e.g., for decompressing a nerve root with alumbar discectomy. For example, as described above in relation to FIGS.18–20, a percutaneous penetration can be made in the patient's back sothat the superior lamina can be accessed. Typically, a small needle isused initially to localize the disc space level, and a guide wire isinserted and advanced under lateral fluoroscopy to the inferior edge ofthe lamina. Sequential cannulated dilators can be inserted over theguide wire and each other to provide a hole from the incision to thelamina. The first dilator may be used to “palpate” the lamina, assuringproper location of its tip between the spinous process and facet complexjust above the inferior edge of the lamina. A tubular retractor can thenbe passed over the largest dilator down to the lamina. The dilators canthen be removed, so as to establish an operating corridor within thetubular retractor. It should be appreciated however, that otherconventional or proprietary methods can be used to access the targetintervertebral disc. Once the target intervertebral disc has beenaccessed, an introducer device may be inserted into the intervertebraldisc.

With reference to FIG. 41, in one embodiment, both introducer needle 928and a second or ancillary introducer 938 may be inserted into the samedisc, to allow introduction of an ancillary device 940 into the targetdisc via ancillary introducer 938. Ancillary device 940 may comprise,for example, a fluid delivery device, a return electrode, an aspirationlumen, a second electrosurgical probe, or an endoscope having an opticalfiber component. Each of introducer needle 928 and ancillary introducer938 may be advanced through the annulus fibrosus until at least thedistal end portion of each introducer 928 and 938, is positioned withinthe nucleus pulposus. Thereafter, shaft 902″ of electrosurgical probe900′ may be inserted through at least one of introducers 928, 938, totreat the intervertebral disc. Typically, shaft 902″ of probe 900′ hasan outer diameter no larger than about 7 French (1 Fr: 0.33 mm), andpreferably between about 6 French and 7 French.

Prior to inserting electrosurgical probe 900 into the intervertebraldisc, an electrically conductive fluid can be delivered into the diskvia a fluid delivery assembly (e.g., ancillary device 940) in order tofacilitate or promote the Coblation® mechanism within the disc followingthe application of a high frequency voltage via probe 900′. By providinga separate device (940) for fluid delivery, the dimensions ofelectrosurgical probe 900′ can be kept to a minimum. Furthermore, whenthe fluid delivery assembly is positioned within ancillary introducer938, electrically conductive fluid can be conveniently replenished tothe interior of the disc at any given time during the procedure.Nevertheless, in other embodiments, the fluid delivery assembly can bephysically coupled to electrosurgical probe 900′.

In some methods, a radiopaque contrast solution (not shown) may bedelivered through a fluid delivery assembly so as to allow the surgeonto visualize the intervertebral disc under fluoroscopy. In someconfigurations, a tracking device 942 can be positioned on shaft distalend portion 902″a. Additionally or alternatively, shaft 902″ can bemarked incrementally, e.g., with depth markings 903, to indicate to thesurgeon how far the active electrode is advanced into the intervertebraldisc. In one embodiment, tracking device 942 includes a radiopaquematerial that can be visualized under fluoroscopy. Such a trackingdevice 942 and depth markings 903 provide the surgeon with means totrack the position of the active electrode 910 relative to a specifictarget site within the disc to which active electrode 910 is to beguided. Such specific target sites may include, for example, an annularfissure, a contained herniation, or a fragment of nucleus pulposus. Thesurgeon can determine the position of the active electrode 910 byobserving the depth markings 903, or by comparing tracking deviceoutput, and a fluoroscopic image of the intervertebral disc to apre-operative fluoroscopic image of the target intervertebral disc.

In other embodiments, an optical fiber (not shown) can be introducedinto the disc. The optical fiber may be either integral with probe 900′or may be introduced as part of an ancillary device 940 via ancillaryintroducer 938. In this manner, the surgeon can visually monitor theinterior of the intervertebral disc and the position of active electrode910.

In addition to monitoring the position of the distal portion ofelectrosurgical probe 900′, the surgeon can also monitor whether theprobe is in Coblation® mode. In most embodiments, power supply 28 (e.g.,FIG. 1) includes a controller having an indicator, such as a light, anaudible sound, or a liquid crystal display (LCD), to indicate whetherprobe 900′ is generating a plasma within the disc. If it is determinedthat the Coblation® mechanism is not occurring, (e.g., due to aninsufficiency of electrically conductive fluid within the disc), thesurgeon can then replenish the supply of the electrically conductivefluid to the disc.

FIG. 42 is a side view of an electrosurgical probe 900′ including shaft902″ having tracking device 942 located at distal end portion 902″a.Tracking device 942 may serve as a radiopaque marker adapted for guidingdistal end portion 902″a within a disc. Shaft 902″ also includes atleast one active electrode 910 disposed on the distal end portion 902″a.Preferably, electrically insulating support member or collar 916 ispositioned proximal of active electrode 910 to insulate active electrode910 from at least one return electrode 918. In most embodiments, thereturn electrode 918 is positioned on the distal end portion of theshaft 902″ and proximal of the active electrode 910. In otherembodiments, however, return electrode 918 can be omitted from shaft902″, in which case at least one return electrode may be provided onancillary device 940, or the return electrode may be positioned on thepatient's body, as a dispersive pad (not shown).

Although active electrode 910 is shown in FIG. 42 as comprising a singleapical electrode, other numbers, arrangements, and shapes for activeelectrode 910 are within the scope of the invention. For example, activeelectrode 910 can include a plurality of isolated electrodes in avariety of shapes. Active electrode 910 will usually have a smallerexposed surface area than return electrode 918, such that the currentdensity is much higher at active electrode 910 than at return electrode918. Preferably, return electrode 918 has a relatively large, smoothsurfaces extending around shaft 902″ in order to reduce currentdensities in the vicinity of return electrode 918, thereby minimizingdamage to non-target tissue.

While bipolar delivery of a high frequency energy is the preferredmethod of debunking the nucleus pulposus, it should be appreciated thatother energy sources (i.e., resistive, or the like) can be used, and theenergy can be delivered with other methods (i.e., monopolar, conductive,or the like) to debulk the nucleus.

FIG. 43A shows a steerable electrosurgical probe 950 including a shaft952, according to another embodiment of the invention. Preferably, shaft952 is flexible and may assume a substantially linear configuration asshown. Probe 950 includes handle 904, shaft distal end 952 a, activeelectrode 910, insulating collar 916, and return electrode 918. As canbe seen in FIG. 43B, under certain circumstances, e.g., upon applicationof a force to shaft 952 during guiding or steering probe 950 during aprocedure, shaft distal end 952 a can adopt a non-linear configuration,designated 952′a. The deformable nature of shaft distal end 952′a allowsactive electrode 910 to be guided to a specific target site within adisc.

FIG. 44 shows steerable electrosurgical probe 950 inserted within thenucleus pulposus of an intervertebral disc. An ancillary device 940 andancillary introducer 928 may also be inserted within the nucleuspulposus of the same disc. To facilitate the debulking of the nucleuspulposus adjacent to a contained herniation, shaft 952 (FIG. 43A) can bemanipulated to a non-linear configuration, represented as 952′.Preferably, shaft 955/952′ is flexible over at least shaft distal end952 a so as to allow steering of active electrode 910 to a positionadjacent to the targeted disc abnormality. The flexible shaft may becombined with a sliding outer shield, a sliding outer introducer needle,pull wires, shape memory actuators, and other known mechanisms (notshown) for effecting selective deflection of distal end 952 a tofacilitate positioning of active electrode 910 within a disc. Thus, itcan be seen that the embodiment of FIG. 44 may be used for the targetedtreatment of annular fissures, or any other disc abnormality in whichCoblation® is indicated.

In one embodiment shaft 952 has a suitable diameter and length to allowthe surgeon to reach the target disc or vertebra by introducing theshaft through the thoracic cavity, the abdomen or the like. Thus, shaft952 may have a length in the range of from about 5.0 cm to 30.0 cm, anda diameter in the range of about 0.2 mm to about 20 mm. Alternatively,shaft 952 may be delivered percutaneously in a posterior lateralapproach. Regardless of the approach, shaft 952 may be introduced via arigid or flexible endoscope. In addition, it should be noted that themethods described with reference to FIGS. 41 and 44 may also beperformed in the absence of ancillary introducer 938 and ancillarydevice 940.

Although the invention has been described primarily with respect toelectrosurgical treatment of intervertebral discs, it is to beunderstood that the methods and apparatus of the invention are alsoapplicable to the treatment of other tissues, organs, and bodilystructures. For example, the principle of the “S-curve” configuration ofthe invention may be applied to any medical system or apparatus in whicha medical instrument is passed within an introducer device, wherein itis desired that the distal end of the medical instrument does notcontact or impinge upon the introducer device as the instrument isadvanced from or retracted within the introducer device. The introducerdevice may be any apparatus through which a medical instrument ispassed. Such a medical system or apparatus may include, for example, acatheter, a cannula, an endoscope, and the like. Thus, while theexemplary embodiments of the present invention have been described indetail, by way of example and for clarity of understanding, a variety ofchanges, adaptations, and modifications will be obvious to those ofskill in the art. Therefore, the scope of the present invention islimited solely by the appended claims.

1. A medical apparatus comprising a shaft including a shaft distal endportion and a shaft proximal end portion, the shaft distal end portionincluding at least one active electrode disposed thereon and having ashape comprising at least one curve proximal to the at least one activeelectrode, wherein the at least one curve comprises a first curve and asecond curve proximal to the first curve, and the shaft distal endportion is adapted to be resilient such that upon the application of anexternal force the shape distorts, whereupon removal of the force theshape restores; further including an introducer needle having a needlelumen, the needle lumen adapted for passing the shaft distal end portiontherethrough, wherein the shaft distal end portion includes a distallinear portion, the active electrode includes an electrode head locatedterminally at a distal tip of the shaft, the first curve ischaracterized by a first angle and the second curve is characterized bya second angle, wherein a transverse location of the electrode headwithin the needle lumen is determined by the first angle and by a lengthof the distal linear portion.
 2. The apparatus of claim 1, wherein theintroducer needle includes a needle distal end, and the shaft distal endportion avoids contact with the introducer needle when the shaft distalend portion is advanced from and retracted into the needle distal end.3. The apparatus of claim 1, wherein the apparatus is adapted forablating tissue during an electrosurgical procedure, the at least onecurve defines a specific curvature of the shaft, the specific curvatureis provided during manufacture of the apparatus, and the specificcurvature is at least substantially maintained during ablation of thetissue.
 4. The apparatus of claim 1, wherein the at least one activeelectrode includes an electrode head having a spike.
 5. The apparatus ofclaim 4, wherein the electrode head includes an apical spike and asubstantially equatorial cusp.
 6. The apparatus of claim 1, wherein theat least one active electrode includes a filament and an electrode head,and the apparatus further comprises a first insulating sleeve encasingthe filament, and an insulating collar disposed on a distal end of thefirst insulating sleeve and adjacent to the electrode head.
 7. Theapparatus of claim 6, further comprising a cylindrical return electrodeon the first insulating sleeve, the return electrode located proximal tothe insulating collar.
 8. The apparatus of claim 7, further comprising asecond insulating sleeve encasing a proximal portion of the returnelectrode.
 9. The apparatus of claim 8, further comprising a shaftshield encasing at least a proximal portion of the second insulatingsleeve, wherein the apparatus is adapted for connection to a powersupply unit via a connector cable, the connector cable includes anelectrically conductive cable shield, and the shaft shield is coupled tothe cable shield.
 10. The apparatus of claim 6, wherein the insulatingcollar comprises a material selected from the group consisting of: aglass, a ceramic, and a silicone.
 11. The apparatus of claim 1, furthercomprising at least one depth marking located at the shaft proximal endportion.
 12. The apparatus of claim 11, wherein the at least one depthmarking comprises a radiopaque material.
 13. The apparatus of claim 1,further comprising a tracking device located at the shaft distal endportion.
 14. An electrosurgical probe and introducer needle combinationfor treating an intervertebral disc, comprising: a probe including ashaft, the shaft including a shaft distal end, at least one activeelectrode, and at least one return electrode, wherein the shaft distalend includes a first curve and a second curve proximal to the firstcurve; and an introducer needle having a lumen and a needle distal end,the introducer needle adapted for passing the shaft distal end throughthe lumen, and for guiding the shaft distal end distally beyond theneedle distal end.
 15. The combination of claim 14, wherein the shaftfurther includes a shaft proximal end portion, the proximal end portionbeing essentially linear, and the first curve and the second curve arein the same plane relative to a longitudinal axis of the proximal endportion of the shaft.
 16. The combination of claim 15, wherein the firstcurve and the second curve are in opposite directions relative to thelongitudinal axis of the proximal end portion of the shaft.
 17. Thecombination of claim 15, wherein the second curve causes a deflection ofthe shaft distal end away from the longitudinal axis of the proximal endportion of the shaft when the second curve is advanced distally beyondthe needle distal end.
 18. The combination of claim 17, wherein thesecond curve is characterized by a second angle, the first curve and thesecond curve are separated by a substantially linear inter-curveportion, and the magnitude of the deflection is determined by the secondangle and a length of the inter-curve portion.
 19. The combination ofclaim 14, wherein the first curve and the second curve are separated bya substantially linear inter-curve portion.
 20. The combination of claim14, wherein the diameter of the lumen is from about 105% to about 500%of the diameter of the shaft distal end.
 21. The combination of claim14, wherein the shaft distal end remains substantially centrally locatedwithin the lumen when the shaft distal end is passed within the lumen.22. The combination of claim 14, wherein the shaft distal end is locatedsubstantially centrally within the lumen when the shaft distal end isretracted into the needle distal end.
 23. The combination of claim 14,wherein the shaft has a length in the range of from about 10 cm to about25 cm, and a diameter in the range of from about 0.5 mm to about 2.5 mm,and the introducer needle has a length in the range of from about 10 cmto about 20 cm, and the lumen has a diameter in the range of from about1.0 mm to about 3.0 mm.
 24. The combination of claim 14, wherein the atleast one active electrode is disposed at a distal tip of the shaft, theshaft distal end includes a distal linear portion, and a transverselocation of the at least one active electrode within the lumen isdetermined by a length of the distal linear portion.
 25. The combinationof claim 14, wherein the at least one active electrode is disposed at adistal tip of the shaft, the first curve is characterized by a firstangle, and the first angle determines a transverse location of the atleast one active electrode within the lumen.
 26. The combination ofclaim 14, wherein the shaft includes a mechanical stop, and themechanical stop limits distal movement of the shaft within the lumen ofthe introducer needle.
 27. A medical apparatus, comprising: a shaftincluding a shaft distal tip, a shaft distal end portion, and a shaftproximal end portion, the shaft distal end portion having a first curveand a second curve proximal to the first curve, wherein the first curveand the second curve are in the same plane relative to a longitudinalaxis of the proximal end portion of the shaft, and the first curve andthe second curve are in opposite directions, and an introducer devicehaving a lumen and an introducer distal end, the introducer deviceadapted for passing the shaft distal end portion through the lumen,wherein the shaft distal tip occupies a substantially central transverselocation within the lumen when the shaft distal end portion is passedwithin the lumen.
 28. The medical apparatus of claim 27, wherein theshaft distal tip occupies a substantially central transverse locationwithin the lumen when the shaft distal end portion is advanced from andretracted into the introducer distal end.
 29. The medical apparatus ofclaim 27, wherein the shaft distal end portion avoids contact with theintroducer device when the shaft distal end portion is advanced from andretracted into the introducer distal end.
 30. The medical apparatus ofclaim 27, wherein the shaft includes a distal linear portion, and atransverse location of the shaft distal tip within the lumen isdetermined by an angle of the first curve and by a length of the distallinear portion.
 31. The medical apparatus of claim 27, wherein thesecond curve causes a deflection of the shaft distal tip away from alongitudinal axis of the shaft when the second curve is advanceddistally beyond the introducer distal end.
 32. The medical apparatus ofclaim 27, further comprising an electrosurgical probe, wherein theelectrosurgical probe includes the shaft.
 33. The medical apparatus ofclaim 27, comprising a medical instrument selected from the groupconsisting of: a catheter, a cannula, an endoscope, and a hypodermicneedle.
 34. The apparatus of claim 27, further comprising a trackingdevice located at the shaft distal end portion, and wherein saidtracking device comprises a material selected from the group consistingof tungsten, stainless steel alloys, platinum, platinum alloys,titanium, titanium alloys, molybdenum, molybdenum alloys, nickel, andnickel alloys.
 35. A medical apparatus, comprising: a shaft including ashaft distal tip, a shaft distal end portion, and a shaft proximal endportion, the shaft distal end portion having a first curve and a secondcurve proximal to the first curve, wherein the first curve and thesecond curve are in the same plane relative to a longitudinal axis ofthe proximal end portion of the shaft, and the first curve and thesecond curve are in opposite directions, and where the shaft distal endportion is adapted to be resilient such that upon the application of anexternal force the at least one curve distorts, whereupon removal of theforce the at least one curve restores, further comprising an introducerdevice having a lumen and an introducer distal end, the introducerdevice adapted for passing the shaft distal end portion through thelumen, wherein the shaft distal tip occupies a substantially centraltransverse location within the lumen when the shaft distal end portionis passed within the lumen.
 36. The medical apparatus of claim 35,wherein the shaft distal tip occupies a substantially central transverselocation within the lumen when the shaft distal end portion is advancedfrom and retracted into the introducer distal end.
 37. The medicalapparatus of claim 35, wherein the shaft distal end portion avoidscontact with the introducer device when the shaft distal end portion isadvanced from and retracted into the introducer distal end.
 38. Themedical apparatus of claim 35, wherein the shaft includes a distallinear portion, and a transverse location of the shaft distal tip withinthe lumen is determined by an angle of the first curve and by a lengthof the distal linear portion.
 39. The medical apparatus of claim 35,wherein the second curve causes a deflection of the shaft distal tipaway from a longitudinal axis of the shaft when the second curve isadvanced distally beyond the introducer distal end.
 40. The medicalapparatus of claim 35, further comprising an electrosurgical probe,wherein the electrosurgical probe includes the shaft.
 41. The medicalapparatus of claim 35, comprising a medical instrument selected from thegroup consisting of: a catheter, a cannula, an endoscope, and ahypodermic needle.
 42. The apparatus of claim 35, wherein the proximalend portion is essentially linear, and the first curve and the secondcurve arc in the same plane relative to the longitudinal axis of theproximal end portion of the shaft, and the first curve and the secondcurve arc in opposite directions relative to the longitudinal axis ofthe proximal end portion of the shaft.
 43. The apparatus of claim 35,further comprising a tracking device located at the shaft distal endportion and comprising a material selected from the group consisting oftitanium alloys and nickel alloys.